CN110869696A - Vibration-resistant white light interference microscope and vibration influence removing method thereof - Google Patents
Vibration-resistant white light interference microscope and vibration influence removing method thereof Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02041—Interferometers characterised by particular imaging or detection techniques
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
- G01B11/2441—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures using interferometry
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02055—Reduction or prevention of errors; Testing; Calibration
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/0209—Low-coherence interferometers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/04—Measuring microscopes
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B21/00—Microscopes
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B21/00—Microscopes
- G02B21/0004—Microscopes specially adapted for specific applications
- G02B21/0016—Technical microscopes, e.g. for inspection or measuring in industrial production processes
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B21/00—Microscopes
- G02B21/0004—Microscopes specially adapted for specific applications
- G02B21/002—Scanning microscopes
- G02B21/0024—Confocal scanning microscopes (CSOMs) or confocal "macroscopes"; Accessories which are not restricted to use with CSOMs, e.g. sample holders
- G02B21/0052—Optical details of the image generation
- G02B21/0056—Optical details of the image generation based on optical coherence, e.g. phase-contrast arrangements, interference arrangements
Abstract
The invention relates to a vibration-tolerant white light interference microscope and a vibration influence removing method thereof, wherein the vibration-tolerant white light interference microscope comprises the following components: a light source section for simultaneously generating a white light having a relatively wide spectrum and a laser light having a relatively narrow spectrum; an interference pattern generating unit including a lens unit and a scanning driving unit for driving the lens unit, the interference pattern generating unit being configured to form an interference pattern of the white light and an interference pattern of the laser light; an illumination imaging microscope optical unit for separating the interference fringes of the white light and the interference fringes of the laser light; a trigger generation unit including a photodiode for measuring an interference pattern of the laser light and a field programmable gate array controller for analyzing the interference pattern of the laser light measured by the photodiode to generate a trigger; a high-speed camera for measuring the interference fringes of the white light; and a control unit for calculating and processing interference pattern measurement information of the white light measured by the high-speed camera.
Description
Technical Field
The invention relates to a vibration-resistant white light interference microscope and a vibration influence removing method thereof.
Background
A white light interference microscope is a device that measures a height difference on a surface of a measurement object in a relatively rapid time by using interference fringes generated between reference lights reflected from reference mirrors by dividing a light path into a measurement sample and the reference mirror direction using a semi-transparent mirror.
Specifically, the white light interference microscope is not affected by measurement errors due to 2 pi ambiguity, which is a drawback of a Phase Shift Interferometer (PSI), and has an advantage of a non-contact Area (Area) measurement method by overcoming a contact point (point) measurement method such as a stylus pen determination, whereby the heights of a plurality of points can be measured at one time.
In addition, in the white light interference microscope, when scanning the z-axis in a high-precision measurement method, vibration occurring in the device or the bottom portion affects an Optical Path Difference (OPD) and causes a measurement error. In this case, the measurement repetition degree is also affected by fine vibration in the process of measuring the nano unit.
In particular, in a mass production line site, bottom vibration transmitted through peripheral equipment and vibration generated in a peripheral motor device such as an air conditioner and transmitted as sound waves have a serious effect. Therefore, even if an expensive device such as an Isolator (Isolator) is used, it is difficult to cut off the vibration, and excessive cost is incurred.
A conventional white light interference microscope transmits a trigger (triggering) signal to an imaging head every time a scanning drive unit scanner moves a predetermined distance (for example, 72nm) in a z-axis to acquire an image. The scanner driving unit is an expensive component, and the control of the moving distance is extremely precise. However, in the case of vibration, even if the scanner of the scan driving unit moves a predetermined distance in the z-axis direction, the probability that the objective lens and the sample move by a distance different from this is high.
In particular, in a mass production apparatus, when a measuring apparatus is attached to a Gantry (Gantry) and a sample having a wide area is moved to a plurality of positions to measure the sample, the movement of the Gantry and the movement of a table supporting the sample due to vibration are independent of each other.
As described above, even if the movement of the scanner of the scan driving unit attached to the z-axis of the measuring instrument of the gantry is precisely controlled, the distance between the objective lens of the measuring instrument and the measurement sample becomes irregular due to vibration.
In this case, the white light interference microscope acquires and analyzes an image every time the distance between the measurement light whose distance between the objective lens and the sample reciprocates and the reference light whose distance between the objective lens and the mirror attached to the objective lens reciprocates changes at a predetermined interval.
Therefore, when an image is acquired at a position where the difference in the optical paths of the reference light and the measurement light exceeds a known equal pitch by vibration, precise distance analysis cannot be performed, and when the vibration is severe, measurement cannot be performed.
Recently, various methods for solving the above-described problems have been proposed, but there are problems in that the device structure becomes complicated or compensation of a predetermined frequency or more cannot be achieved due to compensation delay.
The prior art related to the present invention includes korean laid-open patent publication No. 10-2008-0051969 (published 2008/06/11), and the above prior art documents disclose technical contents related to a white light scanning interferometer and a shape measuring method.
Disclosure of Invention
Problems to be solved by the invention
The present invention has an object to provide a vibration-tolerant white-light interference microscope in which a high-coherence laser interferometer is added to the optical path of a conventional white-light interference microscope, and a trigger can be provided to a camera whenever the optical path difference between reference light and measurement light changes by a predetermined interval regardless of vibration during scanning.
Another object of the present invention is to provide a method for removing the influence of vibration of the vibration-resistant white-light interference microscope.
The object of the present invention is not limited to the above-mentioned object, and other objects and advantages of the present invention which are not mentioned can be understood by the following description, and are more apparent from the embodiments of the present invention. Also, the objects and advantages of the present invention can be easily achieved by the embodiments and the combinations thereof as embodied in the claims.
Means for solving the problems
In order to achieve the above object, a vibration-tolerant white light interference microscope according to an embodiment of the present invention includes: a light source section for simultaneously generating a white light having a relatively wide spectrum and a laser light having a relatively narrow spectrum; an interference pattern generating unit including a lens unit and a scanning driving unit for driving the lens unit, the interference pattern generating unit being configured to form an interference pattern of the white light and an interference pattern of the laser light; an illumination imaging microscope optical unit for separating the interference fringes of the white light and the interference fringes of the laser light; a trigger generation unit including a photodiode for measuring an interference pattern of the laser light and a field programmable gate array controller for analyzing the interference pattern of the laser light measured by the photodiode to generate a trigger; a high-speed camera for measuring the interference fringes of the white light; and a control unit for calculating and processing interference pattern measurement information of the white light measured by the high-speed camera.
The light source unit includes: a white light generator for generating the white light; and a laser generating section for generating the laser beam.
The white light generating unit includes at least one white lamp, and the laser light generating unit includes at least one laser diode.
Further, the laser light generated by the laser light generating unit can have high coherence and relatively bright brightness compared to the white light generated by the white light generating unit.
The illumination imaging microscope optical unit may form the separated interference fringes of the white light and the separated interference fringes of the laser light on the high-speed camera and the photodiode.
The illumination imaging microscope optical unit includes a plurality of beam splitters, and the plurality of beam splitters include: a first spectroscope disposed adjacent to the light source unit; and a second beam splitter disposed adjacent to the photodiode.
Further, the present invention includes: a first cylindrical mirror positioned between the light source unit and the first spectroscope; and a second cylindrical mirror disposed in the optical system of the illumination imaging microscope and located between the first spectroscope and the second spectroscope.
The lens unit includes one or more of a convex mirror, a reference mirror, and a semi-transparent mirror, and the scan driving unit includes a piezoelectric device for moving the lens unit by receiving an external voltage.
The method for removing the vibration influence of the vibration-tolerant white light interference microscope in another embodiment of the invention comprises the following steps: a step (a) of generating white light and laser light by the light source unit, forming interference fringes of the white light and interference fringes of the laser light by the interference fringe generating unit, and separating the interference fringes of the white light and the interference fringes of the laser light by the illumination imaging microscope optical unit, wherein the white light is imaged by the high-speed camera and the laser light is imaged by the photodiode; analyzing the interference fringes of the laser measured by the photodiode in the field programmable gate array controller, wherein the field programmable gate array controller provides a trigger to the high-speed camera to remove vibration; and (c) measuring interference fringes of the white light in the high-speed camera receiving the trigger.
In this case, the method further includes, before the step (a), a step (a-1) of measuring vibrations of a head and a measurement target of the white light interference microscope and setting a driving speed of the scanning driving unit and an imaging speed of the high-speed camera, wherein the step (a-1) includes: measuring vibrations of a head and a measurement object of the white light interference microscope with a vibration meter, and analyzing the measured vibrations to obtain a maximum speed of the vibrations; and setting a driving speed of the scanning driving unit and a photographing speed of the high-speed camera, which are greater than a maximum speed of the vibration.
Effects of the invention
According to the present invention, the high-coherence laser interferometer is added to the optical path of the conventional white light interference microscope, and the influence of the vibration-tolerant white light interference microscope can be removed by providing a trigger to the camera whenever the optical path difference between the reference light and the measurement light changes by a predetermined interval regardless of the vibration during the scanning. Accordingly, since the trigger is given while the actual distance is being observed, the specification of the scan driving unit is not so high, and the extra cost is not additionally required, which is economically advantageous.
In addition to the above-described effects, the specific effects of the present invention will be described together in the following description of specific matters for carrying out the invention.
Drawings
FIG. 1 is a schematic view schematically showing a vibration-fast white-light interference microscope according to an embodiment of the present invention.
Fig. 2 is a graph exemplarily showing the high coherence interference signal and the camera trigger occurrence position in the case (a) where there is no vibration and the case (b) where there is vibration in the vibration-fast white light interference microscope according to the embodiment of the present invention.
FIG. 3 is a diagram illustrating an example of a high coherence interference signal when there is vibration in a vibration tolerant white light interference microscope according to an embodiment of the present invention: graph of interference waveform and phase when vibration was carried out at Vp 13 μm/s and 4Hz 498nm amplitude (Class C).
FIG. 4 is a diagram illustrating the results of a high coherence interference signal when there is vibration in a vibration tolerant white light interference microscope according to an embodiment of the present invention: vp 13 μm/s, 4Hz and 995nm amplitude (2 times of Class C) and its phase.
FIG. 5 is a diagram illustrating the results of a high coherence interference signal when there is vibration in a vibration tolerant white light interference microscope according to an embodiment of the present invention: vp is 26 μm/s, 4Hz and 995nm amplitude (2 times of Class C) and its phase.
Detailed Description
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art to which the present invention pertains can easily carry out the present invention. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.
Parts that are not related to the description are omitted for the sake of clarity, and the same reference numerals are given to the same or similar components throughout the specification. Further, some embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the process of assigning reference numerals to constituent elements in the respective drawings, the same constituent elements are assigned the same reference numerals as much as possible even if presented in different drawings. In describing the present invention, if it is determined that a detailed description of a related known structure or function does not make the gist of the present invention unclear, a detailed description thereof will be omitted.
In describing the components of the present invention, terms such as first, second, A, B, (a), (b), and the like may be used. Such terms are used only to distinguish two kinds of structural elements, and the nature, order, sequence, number, or the like of the corresponding structural elements is not limited to the above terms. In the case where one constituent element is "connected", "coupled" or "coupled" to another constituent element, the constituent element may be directly connected or coupled to the other constituent element, the other constituent element may be "formed" between the constituent elements, or the constituent elements may be "connected", "coupled" or "coupled" to the other constituent element.
In the process of embodying the present invention, for the sake of convenience of description, it is possible to describe the components by being subdivided, and these components may be embodied in one device or module, or one component may be embodied in a plurality of components.
The white light interference microscope has an advantage of having a non-contact area measurement method by overcoming the contact point measurement method determination such as a touch pen without being affected by a measurement error due to 2 pi ambiguity which is a drawback of the phase shift interferometer.
However, in the case where vibration generated in the apparatus or the bottom portion affects the optical path difference in the high-precision measurement method, the white light interference microscope affects the optical path difference when scanning the z-axis, and causes a measurement error. In other words, in the process of measuring the nano-unit, the minute vibration also affects the measurement repetition degree.
In order to solve the above problems, the present invention proposes that a high-coherence laser interferometer is added to the optical path of a conventional white light interference microscope. Thus, during scanning, regardless of vibration, the line camera provides a trigger whenever the optical path difference between the conventional light and the measurement light changes by a predetermined interval. This can eliminate the influence of vibration of the white light interference microscope.
Hereinafter, a vibration-tolerant white-light interference microscope and a vibration influence removing method thereof according to an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic view schematically showing a vibration-fast white-light interference microscope according to an embodiment of the present invention.
Referring to fig. 1, the vibration-tolerant white light interference microscope 100 according to the embodiment of the present invention includes a light source unit 110, an illumination imaging microscope optical unit 130, an interference fringe generating unit 150, a trigger generating unit 170, and a control unit 190.
The light source unit 110 includes a white light generation unit 111 and a laser light generation unit 113.
The White light generating unit 111 is a White Lamp (White Lamp) for measurement and generates light having a wide spectrum.
The Laser light generating section 113 may include a Laser Diode (Laser Diode) for generating light having a narrower spectrum than the white light generating section 111.
The laser light generating unit 113 generates high-coherence and bright light.
Unlike white light for measurement, laser light was used for reference confirmation.
The illumination imaging microscope optical unit 130 separates interference fringes of the white light generated in the white light generating unit 111 and interference fringes of the laser light generated in the laser light generating unit 113.
Then, the illumination imaging microscope optical unit 130 separates the interference fringes of the white light and the interference fringes of the laser light to form an image on the high-speed camera 180 and the sensor of the photodiode 171.
The illumination imaging microscope optical unit 130 is provided with a plurality of beam splitters 131 and 133. For convenience of description, the beam splitter disposed on the light source unit 110 side is referred to as a first beam splitter 131, and the beam splitter disposed on the photodiode 171 side is referred to as a second beam splitter 133.
The first and second beam splitters 131 and 133 may be semi-transparent mirrors that reflect a part of the light and transmit a part of the surplus light.
The interference pattern generating unit 150 forms white-light interference patterns and laser interference patterns.
Specifically, the interference pattern generating section 150 includes a lens section 151, a scan driving section 153, and a scan driving section controller 155.
The lens portion 151 is an optical system including one or more of a convex mirror, a reference mirror, and a semi-transparent mirror.
The lens portion 151 may use a known Mirau interferometer, a Michelson interferometer, or the like.
For example, a case where the lens unit 151 is a Mirau interferometer will be described.
As shown in fig. 1, the convex mirror is disposed at the upper portion, and the light is focused on the reference mirror located at the middle portion, and then, the light is reflected by hitting the sample (i.e., the measurement object S) through the semi-transparent mirror disposed at the lower portion. Wherein interference occurs by a difference between a light path reflected at the reference mirror and a light path reflected at the collision sample. As a result, interference fringes are formed.
The scan driving part 153 is a piezoelectric (piezo) device that generates a voltage by receiving a force from the outside or moves by receiving a voltage, and specifically, is a driving device that moves by receiving a voltage.
The scan driving part 153 is used to precisely move the lens part 151.
The scan driving unit controller 155 receives a command signal from a control unit 190 (e.g., a PC) to operate the scan driving unit 153.
On the other hand, at least one tube mirror 121, 123 may be provided at the light source section 110 and the illumination imaging microscope optical section 130.
The tube lens 121 located on the light source unit 110 side is referred to as a first tube lens, and the tube lens 123 located on the illumination and imaging microscope optical unit 130 side is referred to as a second tube lens. These cylindrical mirrors 121, 123 serve as lens members, and light released at one point becomes parallel light, so that light passing in parallel can be collected at one point.
For example, the first barrel mirror 121 is used to form parallel light from light released at a point, and the second barrel mirror 123 is used to collect light passing in parallel at a point.
The trigger generator 170 analyzes the interference fringes of the laser light and confirms an accurate Z-axis value, and when the position to be measured is reached, a trigger can be generated.
As a specific example, the trigger generation section 170 includes a photodiode 171(Photo Diode) and a field programmable gate array controller 173.
The photodiode 171 is used to measure the interference fringes of the laser light. For example, the photodiode 171 as a single pixel device may utilize a device having tens of thousands to tens of millions of fps.
The field programmable gate array controller 173 analyzes the interference fringes of the laser light measured from the photodiode 171 to generate a trigger.
The high-speed camera 180 measures interference fringes of the white light. For example, the high-speed camera 180 may have several tens to several million pixels (pixels), and may measure a wide area of white light interference fringes at one time.
The control unit 190 is a device for calculating and processing image processing and data, and a known PC or the like can be used.
Hereinafter, a method for removing the influence of vibration of a vibration-resistant white-light interference microscope according to an embodiment of the present invention will be described. In the following description, the constituent elements of the apparatus are referred to by reference numerals of fig. 1.
The vibration-tolerant white-light interference microscope 100 adds a laser diode, that is, a high coherence interferometer using a laser light generating unit 113 and a photodiode 171, to the optical path of a conventional white-light interference microscope. During scanning, a trigger is provided to the high-speed camera 180 to remove the influence of vibration every time the path difference between the reference light and the measurement light changes at a prescribed interval regardless of vibration.
Vibration measurement and scan drive unit drive speed setting step
First, the vibration of the head and the measurement object, i.e., the vibration existing in the sample S, of the white light interference microscope is measured by a vibration meter, and the measured vibration is analyzed to determine the maximum speed of the vibration. Then, the driving speed of the scanning driving section 153 is set to be higher than the maximum speed of the vibration. The FPS of the high-speed camera 180 is set according to the driving speed of the scan driving part 153. In this case, the driving speed of the scan driving part 153 is in proportional relation to the high-speed camera 180. The measurement is performed at the set driving speed of the scan driving unit 153 and the imaging speed of the high-speed camera 180. After that, the scan driving part 153 may move at a constant speed.
White light and laser imaging step
White light and laser light are generated in the light source unit 110. The white light and the laser light become parallel light through the first barrel mirror 121. The white light and the laser light that become parallel light collide with the first beam splitter 131, and a part of the light is transmitted and disappears, and the remaining part is reflected in the sample direction and bent.
Then, the white light and the laser light are focused through a convex mirror inside the lens portion 151, and the focus position is formed on a reference mirror.
The white light and the laser light collide with the semi-transparent mirror, and a part thereof faces the reference mirror and a part thereof faces the sample S. The white light and the laser light directed towards the reference mirror and the sample impinge on the reference mirror and the sample to be reflected and directed towards the semi-transparent mirror.
In this case, the white light and the laser light, which collide with the reference mirror and are reflected, collide with the semi-transparent mirror, and a portion thereof is transmitted and disappears, and a portion thereof is reflected and moves in the direction in which the high-speed camera 180 and the photodiode 171 are located.
Further, the white light reflected by the collision sample and the laser light collide with the semi-transparent mirror, and a part thereof is reflected and disappears, and a part thereof is transmitted and moves in the direction in which the high-speed camera 180 and the photodiode 171 are located.
After that, the light moving toward the high-speed camera 180 and the photodiode 171 is condensed and interfered, in which case the intensity of the light is changed according to the light path difference. Also, the light causing interference passes through a convex mirror inside the lens part 151 and becomes parallel light.
On the other hand, the light that becomes parallel light hits the first beam splitter 131 of the illumination imaging microscope optical section 130, a part of which is reflected and disappears, and a part of which is transmitted and moves in the direction in which the high-speed camera 180 and the photodiode 171 are located.
The white light and the laser light transmitted through the first dichroic mirror 131 are focused through the second barrel mirror 123, and the focused position is formed on the high-speed camera 180 and the sensor of the photodiode 171.
The white light and the laser light focused by the second barrel mirror 123 collide with the second beam splitter 133 of the illumination imaging microscope optical section 130, a part of which is reflected and directed toward the photodiode 171, and a part of which is transmitted and directed toward the high-speed camera 180.
As described above, the white light and the laser light are imaged only on the sensors of the high-speed camera 180 and the photodiode 171, respectively, by the second barrel mirror 123.
Laser interference fringe analysis step
The interference fringes of the laser light measured in the photodiode 171 are analyzed in the field programmable gate array controller 173.
If the phase of the interference fringes of the laser corresponds to n pi/2, the field programmable gate array controller 173 provides a trigger to the high-speed camera 180. The vibration n-0, 1, 2, 3, 4, 5 … is removed by providing a trigger to n pi/2).
Measurement procedure of white light interference fringes
The high-speed camera 180 receiving the trigger measures the white light interference fringes at the corresponding instant.
The measured white light interference fringes accumulate over the entire scan interval.
On the other hand, the control unit 190 performs arithmetic processing on information of each pixel of the high-speed camera 180 and analyzes the information. In this case, Fourier Domain Analysis (FDA) may be used for the Analysis. The height information of each pixel is obtained by Fourier domain analysis, and the height difference information is obtained according to the height of each pixel.
On the other hand, fig. 2 to 5 are graphs for explaining the vibration influence removing method of the vibration-enduring white light interference microscope according to the embodiment of the present invention.
The photodiode output signal of the high coherence interferometer using a laser diode is as follows.
However, the presence of OPD 2z cos θin2z (where, theta)inAngle of reference light incident on the sample), and therefore, the following approximation is made.
In the presence of vibration, z has the following value.
And, if IAc(z (t)) is close to a constant, and when vibration is present at last, the output signal of the hanging diode of the high coherence interferometer using a laser diode shows the state of the parts (a) and (b) of fig. 2 according to the vibration as follows.
t: time of day
I (z (t)): final signal
z (t): distance between lens and sample
IDC: magnitude of the average signal
IAC: frequency of interference fringe signal
λref: wavelength of laser diode
z0: distance between lens and sample when t is 0
Vp: velocity of PZT
Ai: amplitude of i vibration
fi: i number of oscillations
In the output signal of the high coherence interferometer, 1fringe is used every time the optical path difference between the reference light and the measuring light is n lambdarefOccurs whenever the actual value of z (t) is λ, regardless of the vibrationrefAnd/2 is presented.
For example, in using λrefIn the case of 520nm, if a trigger is provided at pi/2 intervals of each fringe, as shown in fig. 2, the amplitude can be adjusted to be approximately λ regardless of the vibrationref/8 (at λ)refAbout 65nm in the case of 520 nm) provides the trigger. When a trigger occurs, a low coherence fringe can be determined. When the trigger position is found in the interference signal, real-time processing can be performed by using a CPU or a field programmable gate array.
Obtaining each lambdarefThe/8 signal is similar in length to the center wavelength of the low coherent interference signal (about 570nm) and the wavelength of the high coherent interference signal, and therefore, by Nyquist's theory, a sufficiently low coherent interference signal can be obtained.
When the measurement is performed by the method described above, regardless of the vibration, an image can be acquired every time a predetermined change is made between the reference light and the measurement light, and the measurement can be performed accurately. If the sign of the change rate of the optical path difference between the reference light and the measurement light is changed due to the extreme vibration, the position that has passed through needs to be passed through again. This is because the phase value of the high-coherence interference signal cannot be 1: 1 to I (z (t)), and therefore, the accurate z (t) cannot be obtained.
FIG. 3 is a diagram illustrating an example of a high coherence interference signal when there is vibration in a vibration tolerant white light interference microscope according to an embodiment of the present invention: graph of interference waveform and phase when vibration was carried out at Vp 13 μm/s and 4Hz 498nm amplitude (Class C).
When the phase of the interference waveform shown in fig. 3 is observed, there is a section in which the phase increase is almost stopped, and in the section, the phase increase does not proceed in the reverse direction (in this case, the direction of decrease), and therefore, the search for the trigger position is not affected.
In the vicinity of the above position, the progress of the scanning drive unit 153 (see fig. 1) and the change in the distance between the objective lens and the sample S (see fig. 1) due to the vibration are cancelled out, and z (t) hardly changes, so that the trigger signal does not occur.
When the scanning drive unit 153 (see fig. 1) is the same as the moving direction of the vibration, z (t) rapidly increases, and the occurrence of the trigger becomes fast. Therefore, the maximum number of acquired images per second (FPS) of the high-speed camera 180 (see fig. 1) used is 2 times or more as large as that in the case of no vibration.
FIG. 4 is a diagram illustrating the results of a high coherence interference signal when there is vibration in a vibration tolerant white light interference microscope according to an embodiment of the present invention: vp 13 μm/s, 4Hz and 995nm amplitude (2 times of Class C) and its phase.
When the phase of the interference waveform shown in fig. 4 is observed, there is a section in which the change in phase changes. In the above-described interval, the phase is shifted in the reverse direction (in this case, the direction of decrease), and during the shift in the reverse direction, the phases of 0, pi/2, pi, and 3 pi/2 are exhibited, and the trigger is generated.
Since the position corresponds to the distance between the reference light and the measurement light for obtaining the image during the rapid trigger period, repeated shooting is performed, and when the image is moved in the forward direction again, shooting is performed again, so that three times of shooting occur in the same section.
In the reverse direction movement section, the direction of progress of the scan driving unit 153 (see fig. 1) is opposite to the direction of change in the distance of the sample S (see fig. 1) due to vibration, and when the movement speed due to vibration is faster, the image is again captured at the distance between the reference light and the measurement light captured in advance.
Then, when the moving direction by the vibration is changed, the scanning driving unit 153 (see fig. 1) is the same as the moving direction of the vibration, and z (t) rapidly increases, so that the trigger rapidly occurs, and the position where the image has been captured 2 times is captured.
As described above, when the change in z (t) due to the vibration is larger than the change due to the movement of the scan driving unit 153 (see fig. 1), the measurement cannot be performed. The above-described case is expressed by a mathematical expression, and the case where the time differential value of the phase of the interference signal has a negative value can be expressed by the following expression.
When in use
The speed is as follows.
Wherein, when Vp > 0 is and dt > 0, if
The rate of change of z (t) is reversed and the reverse direction occurs.
However, if
Is always in
The case (1). Thus, satisfy
Conditions are used to prevent the occurrence of the reverse direction progression problem. When the peak velocity of the vibration is higher than the velocity of the scan driving unit 153 (see fig. 1), the vibration may not be removed and the measurement may be performed.
And, if so, satisfy
The measurement can also be performed at higher vibrations.
FIG. 5 is a diagram illustrating the results of a high coherence interference signal when there is vibration in a vibration tolerant white light interference microscope according to an embodiment of the present invention: vp is 26 μm/s, 4Hz and 995nm amplitude (2 times of Class C) and its phase.
Referring to FIG. 5, satisfy
Thereby, the reverse direction does not occur.
If Vp is greater than or equal to 50um/s, ClassB can be measured at 4Hz, and ClassA can be measured at 8Hz or higher, which corresponds to the case where no isolator is provided in a general production line. Therefore, when the above method is applied, accurate measurement is performed using a white light interference microscope in all production lines.
As described above, according to the configuration and operation of the present invention, the present invention has an effect that the high-coherence laser interferometer is added to the optical path of the conventional white light interference microscope, and the influence of the vibration-resistant white light interference microscope can be removed by providing a trigger to the camera whenever the optical path difference between the reference light and the measurement light changes by a predetermined interval during the scanning regardless of the vibration. Accordingly, since the trigger is given while the actual distance is being observed, the specification of the scanner of the scan driving unit is not so high, and the extra cost is not additionally required, which is economically advantageous.
As described above, the present invention is explained with reference to the drawings, and the present invention is not limited to the embodiments and drawings disclosed in the present specification, and various modifications can be made by those skilled in the art to which the present invention pertains within the scope of the technical idea of the present invention. In the description of the embodiments of the present invention, even if the operational effects of the configuration of the present invention are not described explicitly, the effects that can be predicted by the corresponding components need to be recognized.
Claims (10)
1. A vibration-tolerant white light interference microscope, comprising:
a light source section for simultaneously generating a white light having a relatively wide spectrum and a laser light having a relatively narrow spectrum;
an interference pattern generating unit including a lens unit and a scanning driving unit for driving the lens unit, the interference pattern generating unit being configured to form an interference pattern of the white light and an interference pattern of the laser light;
an illumination imaging microscope optical unit for separating the interference fringes of the white light and the interference fringes of the laser light;
a trigger generation unit including a photodiode for measuring an interference pattern of the laser light and a field programmable gate array controller for analyzing the interference pattern of the laser light measured by the photodiode to generate a trigger;
a high-speed camera for measuring the interference fringes of the white light; and
and a control unit for calculating and processing interference pattern measurement information of the white light measured by the high-speed camera.
2. The vibration-tolerant white-light interference microscope according to claim 1, wherein the light source unit includes:
a white light generator for generating the white light; and
and a laser generating unit for generating the laser beam.
3. The vibration-tolerant white light interference microscope of claim 2,
the white light generating part includes at least one white lamp,
the laser generating section includes at least one laser diode.
4. The vibration-tolerant white-light interference microscope of claim 2, wherein the laser light generated in the laser light generating unit has a higher coherence and a relatively bright brightness than the white light generated in the white light generating unit.
5. The vibration-tolerant white-light interference microscope of claim 1, wherein the illumination imaging microscope optical section images the separated interference fringes of the white light and the laser light on the high-speed camera and the photodiode.
6. The vibration-tolerant white light interference microscope of claim 5,
the illumination imaging microscope optical part comprises a plurality of spectroscopes,
the plurality of beam splitters includes:
a first spectroscope disposed adjacent to the light source unit; and
and a second beam splitter disposed adjacent to the photodiode.
7. The vibration-tolerant white light interference microscope of claim 6, comprising:
a first cylindrical mirror positioned between the light source unit and the first spectroscope; and
and a second cylindrical mirror arranged in the optical system of the illumination imaging microscope and positioned between the first spectroscope and the second spectroscope.
8. The vibration-tolerant white light interference microscope of claim 1,
the lens part comprises more than one of a convex lens, a reference lens and a semi-transparent lens,
the scan driving part includes a piezoelectric device for moving the lens part by receiving an external voltage.
9. A vibration influence removing method for a vibration-tolerant white-light interference microscope, which is used for removing the vibration influence of the vibration-tolerant white-light interference microscope of claims 1 to 8, comprising:
a step (a) of generating white light and laser light by the light source unit, forming interference fringes of the white light and interference fringes of the laser light by the interference fringe generating unit, and separating the interference fringes of the white light and the interference fringes of the laser light by the illumination imaging microscope optical unit, wherein the white light is imaged by the high-speed camera and the laser light is imaged by the photodiode;
analyzing the interference fringes of the laser measured by the photodiode in the field programmable gate array controller, wherein the field programmable gate array controller provides a trigger to the high-speed camera to remove vibration; and
and (c) measuring interference fringes of the white light in the high-speed camera receiving the trigger.
10. The method of claim 9, wherein the method of removing the vibration effect of the vibration-tolerant white-light interference microscope,
before the step (a), the method further comprises a step (a-1) of measuring vibrations of the head and the measurement object of the white light interference microscope, setting a driving speed of the scanning driving unit and an imaging speed of the high-speed camera,
the step (a-1) includes:
measuring vibrations of a head and a measurement object of the white light interference microscope with a vibration meter, and analyzing the measured vibrations to obtain a maximum speed of the vibrations; and
and setting a driving speed of the scanning driving unit and a photographing speed of the high-speed camera, which are greater than a maximum speed of the vibration.
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| KR1020180072933A KR102019326B1 (en) | 2018-06-25 | 2018-06-25 | Vibration tolerant white light scanning interferometer and its vibration effect removal method |
| PCT/KR2019/007143 WO2020004838A1 (en) | 2018-06-25 | 2019-06-13 | Vibration-resistant white light interference microscope and method for removing vibration effect thereof |
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| CN117006971A (en) * | 2023-09-25 | 2023-11-07 | 板石智能科技(深圳)有限公司 | Three-dimensional morphology measurement system |
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| CN111220067B (en) * | 2020-02-27 | 2021-07-13 | 中国工程物理研究院机械制造工艺研究所 | Automatic focusing device and method of white light interferometer |
| CN111473742B (en) * | 2020-05-22 | 2021-07-16 | 大连理工大学 | Morphology simulation and compensation method for batwing effect of white light scanning interferometry |
| KR102504845B1 (en) * | 2020-12-17 | 2023-03-02 | 인천대학교 산학협력단 | Apparatus and method for measuring surface topograph of sample |
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