System and method for measuring three-dimensional shape using phase shifting interferometry and afm

Abstract

The present invention relates to a system and a method for measuring a three-dimensional shape using phase shifting interferometry and an AFM and, more specifically, to an apparatus for measuring a three-dimensional shape of an object to be measured through phase shifting interferometry and an AFM, the apparatus being characterized by comprising: a phase shifting interferometry unit for measuring the overall shape of the object to be measured; and an AFM unit for measuring the object to be measured, and measuring the boundary of a specific area of the object to be measured with an active cantilever probe moving through a three-axis piezo actuator.

Description

Three-dimensional shape measurement system and measurement method using phase shift interferometer and AFM

[0001] The present invention relates to a three-dimensional shape measurement system and measurement method using a phase shift interferometer and an AFM.

[0002] Methods for measuring the microscopic surface shape of precision parts include stylus type measurement, scanning electron microscope measurement, scanning probe microscope measurement, phase shifting interferometry measurement, white-light scanning interferometry measurement, and confocal scanning microscope measurement.

[0003] These measurement methods mainly measure geometric shapes on a two-dimensional plane, such as circles, lines, angles, and line widths, or inspect pattern defects, foreign substances, and asymmetry, and are mainly based on probe systems and image processing technologies consisting of optical microscopes, lighting, and imaging elements such as CCD cameras.

[0004] Among these measurement methods, white light scanning interferometry and phase shifting interferometry (PSI) are attracting attention as non-contact measurement methods that are widely applied to three-dimensional measurements of micro-shapes, such as semiconductor pattern measurement, surface roughness measurement of soft materials, ball grid array (BGA) ball measurement, laser marking pattern measurement, and via hole measurement.

[0005] Although these two measurement methods are based on different measurement principles, they can be implemented in the same optical and measurement systems, except that they use multi-wavelength and monochromatic wavelengths, respectively, so they can be used together in commercial measurement systems.

[0006] These measurement methods use optical interference signals, which are expressed as bright or dark light depending on the difference in distance traveled by the two rays of light when they start simultaneously from an arbitrary reference point, travel along different optical paths, and then merge.

[0007] As a prior art document related to this white light interferometer, Korean Patent No. 10-0598572 (July 7, 2006) proposed white-light scanning interferometry (WSI) to measure information on the thickness or surface shape of a transparent thin film layer during the process of applying a transparent thin film layer on the surface of an opaque metal layer during the semiconductor and LCD (Liquid Crystal Display) manufacturing process.

[0008] The basic measurement principle of this white light scanning interferometry is to utilize the short coherence length characteristics of white light, and more specifically, it utilizes the principle that an interference signal is generated only when the reference light and the measurement light, which are separated by a beam splitter, experience almost the same optical path difference. When the measurement target is moved in the direction of the optical axis by a transport means such as a PZT actuator at micro-intervals of several nanometers and the interference signal at each measurement point within the measurement area is observed, a short interference signal is generated at each point where the same optical path difference as the reference mirror occurs, and when the location of occurrence of this interference signal is calculated at all measurement points within the measurement area, information on the 3D shape of the measurement surface is obtained, and the surface shape of the thin film layer is measured from the obtained 3D information.

[0009] A phase-shift imaging interferometer combining phase-shifting technology and ellipsometry has been proposed to measure 2D thickness profiles of thin films. This image processing technique was developed to improve the precision of the interferometer.

[0010] Accordingly, various methods for utilizing phase shifting between two optical beams have been proposed, and a number of phase shifting interferometers have been developed and applied in various fields.

[0011] Phase-shifting interferometry is a well-established technique for area surface characterization that relies on the digitization of interference data acquired during controlled phase shifts, most often introduced by controlled mechanical vibration of an interference objective. This technique provides full 3D images with typical height measurement repeatability of less than 1 nm, regardless of field size. Interferometric microscopes utilize a variety of specialized interference objectives for roughness and micro-topography measurements.

[0012] In the simplest case of normal incidence illumination and viewing, scaling phase data to height data follows the equation reproduced below.

[0013]

[0014] K=4π / λ

[0015]

[0016] K corresponds to the speed at which the interference signal oscillates sinusoidally with respect to the sample surface height h or the reference mirror position. If the geometry is suitable for the low numerical aperture case and the wavelength is known, the measurement is, in principle, self-calibrating according to the measurement principle.

[0017]

[0018] Furthermore, recent advances in nanofabrication technology have enabled the production of active cantilever probes with embedded sensors and actuators. Atomic force microscopes (AFMs) equipped with active probes offer new capabilities and simplified user experience compared to conventional passive probes.

[0019] Conventional cantilever deflection detection is primarily accomplished through external methods, such as an optical beam deflection (OBD) system. In an OBD setup, a monochromatic laser (e.g., a 635 nm wavelength HeNe laser) is focused onto the back of the cantilever's free end.

[0020] Small changes in the angle of the free end of the cantilever are amplified by the reflected ray path length, producing linear motion of the detector that is much larger than the linear motion of the cantilever probe tip.

[0021] The reflected light is directed toward the center of a position detector (typically a four-quadrant photodiode) to detect the movement of the reflected light. Assuming that the laser alignment along the probe lies within a 2D plane, it can be shown that the cantilever deflection Δz is directly proportional to the tip angle.

[0022] Another optical method for detecting cantilever probe deflection is laser interferometry. This approach focuses a laser beam onto the back of the cantilever probe to directly detect displacement.

[0023] Another detection method applies the principle of astigmatism detection.

[0024] It is used in the optical pickup device of a CD / DVD reader to detect cantilever probe deflection. This design mechanism uses a focus error signal proportional to the defocus distance generated by the photodiode to detect the focus state of light reflected from the target through the principle of astigmatism.

[0025] AFM cantilever probe deflection detection can be realized using piezoresistive or piezoelectric sensing. Attempts have also been made to detect opto-mechanical deflection. Advances in semiconductor micro / nanofabrication technology have enabled the integration of micrometer-scale sensors into cantilever probes. Recent designs incorporate multiple piezoresistive elements at the cantilever base, where maximum bending stress occurs. Typically, four piezoresistive elements are used to form a full Wheatstone bridge configuration, improving sensitivity and reducing thermal drift.

[0026] Piezoresistive sensing facilitates embedded measurement of cantilever probe deflection via resistance measurement, enabling both static and dynamic measurements over a wide bandwidth (from DC to megahertz). Its sensitivity is comparable to that of optical methods, but is not limited by the diffraction limit, allowing the use of nanometer-scale cantilevers.

[0027] Modern semiconductor manufacturing technologies allow for sensing element geometric dimensions to be significantly smaller than those of conventional strain gauges, taking miniaturization into account. This reduced installation space allows for specialized probe designs for more accurate lateral force measurements. Therefore, this is the primary method used for embedded cantilever sensing, both externally and internally.

[0028] The fundamental requirement for dynamic mode operation is excitation of the cantilever resonance. Some operating strategies can also control static deflection. Advanced AFM cantilever probes are fabricated by combining built-in self-sensing and self-actuation methods. These probes are called active cantilevers.

[0029] Figure 1 shows an AFM measurement signal for a measurement object, Figure 2 shows an interferometer (PSI) measurement signal for a measurement object, and Figure 3 shows a comparison graph of an AFM measurement signal and a PSI measurement signal in a specific area (Cu area) of the measurement object.

[0030] Figures 4a and 4b show PSI measurement signals in a specific area (Cu area) repeatedly measured using a phase shift interferometer.

[0031] As shown in FIGS. 3 and 4a and 4b, the PSI measurement values ​​within a specific region have high repeatability, but as shown in FIGS. 1 and 2, it can be seen that the error in the PSI measurement signal is high compared to the AFM measurement signal for the boundary part of the specific region. This is due to the difference in extinction coefficient between the specific region (Cu) and the remaining region (SiO2).

[0032] In addition, when measuring an object to be measured using an AFM unit, the accuracy is high, but there is a disadvantage in that it takes a lot of time to measure the entire object.

[0033] Accordingly, the present invention has been made to solve the above-described conventional problems, and according to an embodiment of the present invention, an object can be inspected using a phase shift interferometer imaging mode using a scanning probe microscope, and an improved 3D image can be generated with a typical height measurement repeatability of less than 0.3 nm regardless of the field size, and the purpose is to provide a three-dimensional shape measurement system and measurement method using a phase shift interferometer and an AFM.

[0034] According to an embodiment of the present invention, the purpose is to provide a three-dimensional shape measurement system and measurement method using a phase shift interferometer and an AFM, which can quickly and accurately analyze a measurement target by measuring the overall shape with an interferometer unit and measuring and correcting only an area with a large error value with an AFM unit.

[0035] According to an embodiment of the present invention, the purpose is to provide a three-dimensional shape measurement system and measurement method using a phase shift interferometer and an AFM, which can increase accuracy by aligning the optical axis of the interferometer with the measurement point during AFM measurement, can accurately measure the deflection position of the tip by incorporating a piezoresistive detection sensor and a small actuator into the probe without using a high-brightness beam deflection system, and can perform nano-positioning using a three-axis piezoelectric actuator.

[0036] Meanwhile, the technical tasks to be achieved in the present invention are not limited to the technical tasks mentioned above, and other technical tasks not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0037] The first object of the present invention can be achieved by a three-dimensional shape measurement system using a phase shifting interferometer and an AFM, characterized in that it comprises a phase shifting interferometer unit for measuring the entire shape of the measurement object; and an AFM unit for measuring the measurement object and having an active cantilever probe that is moved by a three-axis piezoelectric actuator and for measuring the boundary of a specific region of the measurement object.

[0038] And when acquiring an interference signal and an AFM signal by an interferometer, it can be characterized in that the AFM measurement point is controlled by a three-axis piezoelectric actuator and aligned with the optical axis of the interferometer.

[0039] In addition, the active cantilever probe of the AFM may be characterized by including: a tip provided on one side of a scanner provided on a frame and provided at an end of a cantilever; an actuator built into the cantilever that deforms the cantilever and drives the tip to press a measurement point; and a piezoresistance detection sensor built inside the cantilever that measures piezoresistance applied to the measurement object by the tip.

[0040] And, one side of the active cantilever probe may protrude outward from the side of the scanner, and the end may be characterized by being tapered downward from the probe body.

[0041] In addition, the actuator may be an electric heating actuator having a bimorph structure and a resistance heating element, and the piezoresistive detection sensor may be characterized by having a Wheatstone bridge structure having four piezoresistive elements and measuring the connection state and contact pressure of the tip.

[0042] And the interferometer unit may be characterized by including: an illumination optical module having a light source that emits light; a polarizing beam splitter that reflects a first polarized wave of the light to make it incident on a reference mirror and transmits a second polarized wave to make it incident on a measurement object; a quarter-wave plate that polarizes the first polarized reflected light reflected from the reference mirror and reflected by the polarizing beam splitter, and the second polarized reflected light reflected from the measurement object and transmitted through the polarizing beam splitter; and a polarizing camera positioned at a rear end of the quarter-wave plate to obtain a plurality of interference images having different polarization states.

[0043] The second object of the present invention can be achieved by a method for measuring a three-dimensional shape of a measurement object using a phase shifting interferometer and an AFM, comprising: a first step in which a phase shifting interferometer unit measures the entire shape of the measurement object within a field of view to obtain an interferometer measurement signal; a second step in which an active cantilever probe is moved to the boundary of a specific region of the measurement object using a three-axis piezoelectric actuator of the AFM unit to measure the boundary of the specific region of the measurement object; and a third step in which a measurement value for the boundary portion is corrected based on the AFM measurement signal.

[0044] And the second step may be characterized by including a second step of positioning the probe tip at a specific measurement point of the boundary area through a three-axis piezoelectric actuator based on the initial position value of the probe tip and the interferometer measurement signal, and aligning the optical axis of the interferometer with the measurement point; a second step of driving an actuator built into the cantilever probe so that the tip presses the measurement point; and a second step of measuring the piezoresistance applied to the measurement point by the tip through a piezoresistance measurement sensor built into the cantilever.

[0045] In addition, the actuator is an electric heating actuator having a bimorph structure and a resistance heating element, and in the second-second step, it may be characterized in that the static bias is controlled by a DC voltage while stimulating the probe resonance with an AC voltage applied to the electric heating actuator.

[0046] And the first step may be characterized by including a step of emitting light from a light source; a step of passing through an illumination optical module and passing through a polarizer as parallel light; a step of reflecting a first polarized wave of light from a polarizing beam splitter and causing it to be incident on a reference mirror, and a step of transmitting a second polarized wave and causing it to be incident on a measurement object; a step of allowing the first polarized reflected light reflected on the reference mirror to be reflected on the polarizing beam splitter, and the second polarized reflected light reflected on the measurement object to pass through the polarizing beam splitter; a step of polarizing the first polarized reflected light and the second polarized reflected light by passing through a quarter-wave plate; and a step of interfering the polarized first polarized reflected light and the second polarized reflected light in a polarizing camera, thereby obtaining a plurality of interference images having different polarization states.

[0047] According to a three-dimensional shape measurement system and measurement method using a phase shifting interferometer and an AFM according to an embodiment of the present invention, an object can be inspected using a phase shifting interferometer imaging mode using a scanning probe microscope, and an improved 3D image can be generated with a typical height measurement repeatability of less than 0.3 nm regardless of the field size.

[0048] According to a three-dimensional shape measurement system and measurement method using a phase shift interferometer and an AFM according to an embodiment of the present invention, the overall shape is measured by an interferometer unit, and only an area with a large error value is measured and corrected by an AFM unit, thereby having the effect of being able to quickly and accurately analyze a measurement target.

[0049] According to a three-dimensional shape measurement system and measurement method using a phase shift interferometer and an AFM according to an embodiment of the present invention, the accuracy can be increased by aligning the optical axis of the interferometer with the measurement point during AFM measurement, the tip deflection position can be accurately measured by incorporating a piezoresistive detection sensor and a small actuator into the probe without using a high-brightness beam deflection system, and nano-positioning is possible through a three-axis piezoelectric actuator.

[0050] Meanwhile, the effects that can be obtained from the present invention are not limited to the effects mentioned above, and other effects that are not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0051] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention, serve to further understand the technical idea of ​​the present invention, and therefore, the present invention should not be interpreted as being limited to matters described in such drawings.

[0052] Figure 1 shows the AFM measurement signal for the measurement target.

[0053] Figure 2 shows the interferometer (PSI) measurement signal for the measurement target.

[0054] Figure 3 is a comparison graph of the AFM measurement signal and the PSI measurement signal in a specific area (Cu area) of the measurement target.

[0055] Figures 4a and 4b are PSI measurement signals in a specific area (Cu area) repeatedly measured by a phase shift interferometer.

[0056] Figure 5 is a flow chart of a three-dimensional shape measurement method using a phase shift interferometer and AFM according to an embodiment of the present invention.

[0057] Figure 6 is a configuration diagram of an interferometer unit according to the first embodiment of the present invention.

[0058] Figure 7 is a configuration diagram of an interferometer unit according to a second embodiment of the present invention.

[0059] Figure 8 is a configuration diagram of an interferometer unit according to a third embodiment of the present invention.

[0060] Figure 9 is a flowchart of an interference signal measurement method according to a third embodiment of the present invention.

[0061] Figure 10 is a configuration diagram of a three-dimensional shape measurement system using a phase shift interferometer and AFM according to an embodiment of the present invention.

[0062] Figure 11 is a schematic diagram and a partially enlarged view of an AFM unit according to an embodiment of the present invention.

[0063] Figure 12 illustrates a flow chart of a measurement method using an AFM unit according to an embodiment of the present invention.

[0064] Below, the configuration, function, and measurement method of a three-dimensional shape measurement system (100) using a phase shift interferometer and AFM according to an embodiment of the present invention will be described.

[0065] The present invention is a three-dimensional shape measuring device for a measurement object using a phase shifting interferometer and an AFM. According to an embodiment of the present invention, the device comprises a phase shifting interferometer unit (1) for measuring the entire shape of the measurement object, and an AFM unit (200) for measuring the measurement object (2) and having an active cantilever probe (150) that moves through a three-axis piezoelectric actuator and measures the boundary of a specific area of ​​the measurement object.

[0066] FIG. 5 is a flowchart illustrating a three-dimensional shape measurement method using a phase shift interferometer and AFM according to an embodiment of the present invention.

[0067] As shown in Fig. 5, first, the entire shape of the measurement target within the field of view is measured through the phase shift interferometer unit to obtain an interferometer measurement signal (e.g., (FOV: 100 um × 100 um) (field of view)) (S10).

[0068] And, by moving the active cantilever probe to the boundary of a specific area of ​​the measurement target through the 3-axis piezo actuator of the AFM unit, the boundary of the specific area of ​​the measurement target is measured (S20). And, based on this AFM measurement signal, the measurement value for the boundary is corrected (S30).

[0069] That is, only the boundary of a specific area (e.g., Cu-SiO2 boundary) is measured using an AFM unit that is moved in parallel by a three-axis (X, Y, Z) piezo actuator to measure the measurement target and align the optical axis of the interferometer unit (1).

[0070] At this time, since the height difference of the Cu-SiO2 region boundary occurring within the same FOV is not expected to vary significantly, it is possible to measure one of the Cu-SiO2 boundaries and adjust it to the same amount. The key to the present invention is that the measurement point of the AFM is identical to the optical axis controlled by the three-axis piezoelectric actuator when acquiring the interference signal and the AFM signal.

[0071]

[0072] Below, the configuration, function, and interference signal measurement method of the interferometer unit according to an embodiment of the present invention will be described first. The first, second, and third embodiments described below are merely preferred embodiments and are not limited thereto.

[0073] Fig. 6 is a block diagram of an interferometer unit according to a first embodiment of the present invention. In the first embodiment of the present invention, some of the light emitted from the light source (10) is reflected through the beam splitter (30) and is incident on the reference mirror (6) side, and the remainder is transmitted and is incident on the measurement object (2) side. After being incident on the reference mirror (6) and the measurement object through the objective lens (40) and reflected, the light reflected on the measurement object (2) is transmitted through the beam splitter (30), and the light reflected on the reference mirror (6) is reflected on the beam splitter (30), and interference occurs through quantum phase delay. The interference signal is measured through the camera (70) through the lens (60).

[0074] Fig. 7 illustrates a configuration diagram of an interferometer unit according to a second embodiment of the present invention. In the second embodiment of the present invention, a reference mirror (6) is not used, and a Mirau objective lens (41) with a built-in Mirau lens is applied.

[0075] That is, in the second embodiment of the present invention, light emitted from a light source (10) is reflected through a beam splitter (30) and is incident on the Mirau objective lens (41), some of which is reflected by the Mirau lens and the remainder is transmitted and is incident on the measurement object (2).

[0076] Interference occurs between the light reflected by the Mirau lens and the light reflected by the measurement object (2), and the interference signal is measured through the lens (60) and the camera (70).

[0077] Fig. 8 illustrates a configuration diagram of an interferometer unit according to a third embodiment of the present invention. In addition, Fig. 9 illustrates a flowchart of an interference signal measuring method according to a third embodiment of the present invention.

[0078] As illustrated in FIG. 8, a one-shot phase shifting interference stereoscopic shape measurement device (100) using a polarization camera according to an embodiment of the present invention may be configured to include an illumination optical module (10), a linear polarizer (13), a beam splitter (21), a polarization beam splitter (20), a reference mirror (2), a quarter-wave plate (QWP) (50), a lens (60), a polarization camera (80), etc.

[0079] In the third embodiment of the present invention, interference images having multiple different polarizations can be obtained with just one measurement.

[0080] According to a third embodiment of the present invention, by using an AF laser to determine the focus position, making the depth sufficiently large within the measurement range of the specimen, and securing an interference distance equivalent to the depth, a polarization camera can be used to acquire four images at once for applying a phase shift algorithm with one image acquisition (one shot), thereby reducing the influence of vibration and enabling rapid measurement.

[0081] In addition, according to a third embodiment of the present invention, by using a polarizer, a quarter-wave plate, and a micro polarizing camera, an image is acquired by continuously moving a measurement object in the X and Y directions through a stage without driving a reference mirror, and 0°, 45°, 90°, and 135° polarization images can be acquired at once through a phase shift algorithm.

[0082] In the third embodiment of the present invention, the device may be configured to include a broadband light source (10) that emits light, and an illumination optical module (11) that emits light so that the light emitted from the broadband light source (10) has a uniform light intensity distribution toward the measurement target (1). As a specific embodiment of the present invention, the broadband light source (10) is configured to emit light having a wavelength of 400 to 700 nm.

[0083] The beam splitter (30) is configured to reflect a portion of the light emitted from the light source (10) and direct it toward the polarizing beam splitter (31).

[0084] The polarizing beam splitter (31) is configured to reflect the first polarized wave of light and transmit the second polarized wave. In other words, it is configured to reflect the S wave and transmit the P wave.

[0085] A linear polarizer (20) is provided between the beam splitter (30) and the illumination optical module (11) so as to be configured to control the ratio of S waves and P waves.

[0086] The first polarized wave reflected by the polarizing beam splitter (31) is reflected by the reference mirror (6) and then reflected again by the polarizing beam splitter (31), while the second polarized wave transmitted is reflected by the measurement object (2) and transmitted to the polarizing beam splitter (31).

[0087] And the quarter-wave plate (50) is configured to polarize the first polarized reflected light reflected from the reference mirror (6) and reflected by the polarizing beam splitter (31), and the second polarized reflected light reflected from the measurement object (2) and transmitted through the polarizing beam splitter (31).

[0088] A phase delay may occur between the first polarized reflected light and the second polarized reflected light by the quarter-wave plate (50), which may generate an interference signal. After passing through the quarter-wave plate (50), the light passes through the lens (60) and enters the polarizing camera (71).

[0089] And the polarization camera (71) is positioned at the rear end of the quarter-wave plate (50) and is configured to acquire multiple interference images having different polarization states.

[0090] And the polarization camera (71) according to the embodiment of the present invention obtains a plurality of interference images in which the first polarized reflected light and the second polarized reflected light interfere with each other and have different polarization states.

[0091] A micro polarization camera (71) according to an embodiment of the present invention comprises a pixelated polarizing plate mask and a 2D sensor array. The pixelated polarizing plate mask comprises a repeated pattern array of 2x2 unit cells for the entire mask.

[0092] And the 2x2 unit cell is a micro-polarizer pattern array having four different polarization axes, and the 2D sensor array is aligned with each individual polarization element of the micro-polarizer pattern array, so that interference images having four different polarization states can be obtained through a polarization camera (71). In addition, the analysis means analyzes the shape of the measurement target from the interference images having different polarization states.

[0093] That is, the analysis means measures and analyzes the three-dimensional shape of the measurement object (2) based on the phase difference between the reflected light of the reference mirror and the reflected light of the measurement object, based on interference images having different polarization states. In addition, the stage is configured to move the measurement object (2) in a planar direction.

[0094]

[0095] Below, the configuration, function, and measurement method of the AFM unit according to an embodiment of the present invention will be described.

[0096] Fig. 10 illustrates a configuration diagram of a three-dimensional shape measurement system (100) using a phase shift interferometer and an AFM according to an embodiment of the present invention. Fig. 11 illustrates a configuration diagram and a partially enlarged view of an AFM unit (200) according to an embodiment of the present invention. Fig. 12 illustrates a flowchart of a measurement method using an AFM unit according to an embodiment of the present invention.

[0097] An active cantilever probe (150) of an AFM unit according to an embodiment of the present invention is used to scan the surface of a measurement object (2) in various AFM measurement modes. In the embodiment, the surface of the measurement object (2) is scanned by the cantilever probe (150) using a three-axis (XYZ) piezo actuator (140) to move the cantilever probe (150) along the X and Y axes.

[0098] It also includes a Z-axis actuator for moving the probe (150) along the Z-axis.

[0099] And, using a three-axis piezo actuator (140), the cantilever is moved along the X, Y, and Z axes through an actuator (152) built into the cantilever probe (150) while the probe (150) is fixed.

[0100] As shown in Fig. 11, it can be seen that the scanner (130) body is installed on the support frame (110), and a Z-axis driving unit for driving the scanner (130) in the Z-axis direction is provided.

[0101] And the active cantilever probe (150) of the AFM is connected to the lower side of the scanner (150). And as shown in the enlarged view of Fig. 11, a tip (151) is provided at the end of the cantilever.

[0102] And the actuator (152) is built into the cantilever and is driven to deform the cantilever so that the tip (151) presses the measurement point. In addition, the piezoresistance detection sensor (153) built into the cantilever is configured to measure the piezoresistance applied to the measurement target (2) by the tip (151).

[0103] And as shown in FIGS. 10 and 11, one side of the active cantilever probe (150) protrudes outward from the side of the scanner (130), and the end is configured to taper downward from the probe body.

[0104] In the AFM unit (200) according to the embodiment of the present invention, when an interference signal and an AFM signal are acquired by an interferometer, the AFM measurement point is controlled by a three-axis piezoelectric actuator (140) to match the optical axis of the interferometer.

[0105] As mentioned above, the phase shift interferometer unit (1) measures the entire shape of the measurement object (2) within the field of view to obtain an interferometer measurement signal.

[0106] And, by moving the active cantilever probe (!50) to the boundary of a specific area of ​​the measurement object (2) through the 3-axis piezo actuator (140) of the AFM unit (200), the boundary of the specific area of ​​the measurement object (20) is measured. And, based on the AFM measurement signal, the measurement value for the boundary portion is corrected.

[0107] Acquisition of an AFM measurement signal through an AFM unit (200) first moves the scanner (130) in the Z-axis direction as a whole through a Z-axis driving unit (120). Then, based on the initial position value of the probe tip (151) and the interferometer measurement signal, the probe tip (151) is positioned at a specific measurement point of the boundary area through a three-axis piezo actuator (140) to the boundary area of ​​a specific area. At this time, the optical axis of the interferometer is aligned with the measurement point (S21).

[0108] And the actuator (152) built into the cantilever probe (150) is driven so that the tip presses the measurement point (S22).

[0109] And, the piezoresistance applied to the measurement point by the tip (151) is measured through the piezoresistance measurement sensor (153) built into the cantilever (S23).

[0110] Additionally, the actuator built into the active cantilever probe (150) may be configured as an electrothermal actuator having a bimorph structure and a resistance heating element.

[0111] Embedded electrothermal actuation of cantilevers utilizes a bimorph structure. This method uses resistive heating elements embedded in the bimorph structure instead of an external laser as a heat source. Electrothermal actuation falls under the category of thermomechanical actuation, where thermally induced mechanical stress causes cantilever bending. The key difference lies in how the temperature change is induced.

[0112] In this case, the temperature change can be quite complex. This is primarily because the heat release rate depends on the temperature difference between the cantilever and the surrounding environment. Typically, the integral of the heating power is proportional to the temperature change. The sinusoidal input excites the probe (150) resonance, while the DC component can be used to control the static deflection of the probe (150). Even if the DC component accumulates in the energy input, the increased heat release power at higher temperatures does not result in an infinite temperature increase.

[0113] In addition, the piezoresistive detection sensor (153) according to an embodiment of the present invention has a Wheatstone bridge structure with four piezoresistive elements and measures the connection state and contact pressure of the tip (151).

[0114] That is, AFM cantilever probe (150) deflection detection can be realized using piezoresistive or piezoelectric detection. Advances in semiconductor micro / nano fabrication technology have made it possible to embed miniature sensors in the cantilever probe (150) in micrometer-scale sizes.

[0115] In an embodiment of the present invention, multiple piezoresistive elements are integrated into the cantilever base, where maximum bending stress occurs. Typically, four piezoresistive elements are used to form a complete Wheatstone bridge configuration, thereby improving sensitivity and reducing thermal drift.

[0116] Piezoresistive sensing facilitates embedded measurement of cantilever probe deflection through resistance measurement, enabling both static and dynamic measurements over a wide bandwidth (from DC to megahertz). Its sensitivity is comparable to that of optical methods, but is not limited by the diffraction limit, enabling the use of nanometer-scale cantilevers. Modern semiconductor manufacturing technologies allow for the geometric dimensions of the sensing element to be significantly smaller than those of conventional strain gauges, taking miniaturization into account. This reduced footprint allows for specialized probe designs for more accurate lateral force measurements.

[0117] A fundamental requirement for dynamic mode operation is the excitation of cantilever resonance. Static deflection can also be controlled using certain operating strategies. The active cantilever probe according to the present invention combines built-in self-sensing and self-actuation methods.

[0118] The active cantilever probe (150) can minimize the physical space of the AFM unit (200) by eliminating the need for bulky external sensing and actuation elements. Embodiments of the present invention include all known probe design examples created primarily for AFM applications utilizing external or built-in sensing and actuation methods.

[0119] Furthermore, various nanotechnology applications require nanopositioning capabilities. Specific positioning requirements can vary significantly depending on the application, including micromanipulation, fiber optic alignment, and wafer-scale lithography. Positioning requirements for AFM operation are characterized by a unique combination of range, bandwidth, and resolution in three orthogonal directions.

[0120] In the embodiments of the present invention, the operation of the AFM nano-positioning system is described using a Cartesian coordinate system. The Z-axis represents the out-of-plane direction in which the sample can bend the cantilever probe (150). The X- and Y-axes correspond to the in-plane directions in which the nano-positioning system scans the probe tip (151) over the sample. In typical raster-style line-by-line imaging, the X-axis is typically aligned with the high-frequency scan line.

[0121] The requirements for an AFM positioning system vary significantly depending on factors such as the type of cantilever probe, the measurement target conditions, and imaging requirements. During AFM imaging, the measurement target (2) or the probe (150) may be moved. Existing AFM systems that utilize optical methods for tip (151) deflection often employ a sample-scan configuration. In this case, the optical components used for the scanning operation are too large, making a sample-scan configuration preferable.

[0122] Implementing an active cantilever probe (150) can simplify the design of a probe (150) scanning AFM system. Combining the object (2) scanning and probe (150) scanning configurations can also improve scanning performance. For general imaging applications, AFM positioning systems are typically designed with a sample scanning configuration that can achieve an in-plane scanning range of up to 100 μm x 100 μm and an out-of-plane Z-axis range of tens of microns by utilizing piezoresistive or optical cantilever readouts.

[0123]

[0124] In addition, the devices and methods described above are not limited to the configurations and methods of the embodiments described above, and the embodiments may be configured by selectively combining all or part of each embodiment so that various modifications can be made.

Claims

1. As a device for measuring the three-dimensional shape of a measurement target using a phase shift interferometer and AFM, A phase shifting interferometer unit that measures the overall shape of the measurement target; and A three-dimensional shape measurement system using a phase shift interferometer and an AFM, characterized in that it includes an AFM unit that measures the measurement object and measures the boundary of a specific area of ​​the measurement object with an active cantilever probe that is moved through a three-axis piezoelectric actuator.

2. In paragraph 1, A three-dimensional shape measurement system using a phase shift interferometer and an AFM, characterized in that when acquiring an interference signal and an AFM signal by the interferometer, the AFM measurement point is controlled by a three-axis piezoelectric actuator to match the optical axis of the interferometer.

3. In paragraph 2, The active cantilever probe of the above AFM is provided on one side of the scanner provided on the frame, A tip provided at the end of the cantilever; An actuator built into the cantilever to deform the cantilever and actuate the tip to press the measurement point; and A three-dimensional shape measurement system using a phase shift interferometer and an AFM, characterized in that it includes a piezoresistance detection sensor built into the cantilever and measuring the piezoresistance applied to the measurement object by the tip.

4. In paragraph 3, A three-dimensional shape measurement system using a phase shift interferometer and an AFM, characterized in that one side of the active cantilever probe protrudes outward from the side of the scanner and the end portion is tapered downward from the probe body.

5. In paragraph 3, The above actuator is an electrothermal actuator having a bimorph structure and a resistance heating element, The above piezoresistive detection sensor has a Wheatstone bridge structure with four piezoresistive elements and is a three-dimensional shape measurement system using a phase shift interferometer and AFM, characterized in that it measures the connection state and contact pressure of the tip.

6. In paragraph 1, The above interferometer unit, An illumination optical module having a light source that emits light; a polarizing beam splitter that reflects a first polarized wave of the light and causes it to be incident on a reference mirror, and transmits a second polarized wave and causes it to be incident on a measurement object; A quarter-wave plate that polarizes the first polarized reflected light reflected from the reference mirror and reflected by the polarizing beam splitter, and the second polarized reflected light reflected from the measurement object and transmitted through the polarizing beam splitter; and A three-dimensional shape measurement system using a phase shift interferometer and an AFM, characterized in that it includes a polarization camera positioned at the rear end of the above quarter-wave plate and obtaining a plurality of interference images having different polarization states.

7. A method for measuring the three-dimensional shape of a measurement target using a phase shift interferometer and AFM. The first step is to obtain an interferometer measurement signal by measuring the entire shape of the measurement target within the field of view using a phase shift interferometer unit; A second step of measuring the boundary of a specific area of ​​the measurement object by moving an active cantilever probe to the boundary of a specific area of ​​the measurement object through a three-axis piezo actuator of the AFM unit; and A three-dimensional shape measurement method using a phase shift interferometer and an AFM, characterized in that it includes a third step of correcting the measurement value for the boundary portion based on the above AFM measurement signal.

8. In paragraph 7, The second step above is, Step 2-1 of positioning the probe tip at a specific measurement point of the boundary area through a three-axis piezoelectric actuator based on the initial position value of the probe tip and the interferometer measurement signal, and aligning the optical axis of the interferometer with the measurement point; Step 2-2 of driving the actuator built into the cantilever probe to press the tip against the measurement point; and A three-dimensional shape measurement method using a phase shift interferometer and an AFM, characterized in that it includes a step 2-3 of measuring the piezoresistance applied to the measurement point by the tip through a piezoresistance measurement sensor built into the cantilever.

9. In paragraph 8, The above actuator is an electrothermal actuator having a bimorph structure and a resistance heating element, A three-dimensional shape measurement method using a phase shift interferometer and AFM, characterized in that in the above step 2-2, the probe resonance is stimulated by an AC voltage applied to the electric heating actuator and the static deflection is controlled by a DC voltage.

10. In paragraph 7, The above first step is, The stage where light is emitted from a light source; A step of passing parallel light through a polarizer while passing through an illumination optical module; A step of reflecting a first polarized wave of light from a polarizing beam splitter and causing it to be incident on a reference mirror, and transmitting a second polarized wave and causing it to be incident on a measurement object; A step in which the first polarized reflected light reflected on the reference mirror is reflected on the polarizing beam splitter, and the second polarized reflected light reflected on the measurement object passes through the polarizing beam splitter; A step in which the first polarized reflected light and the second polarized reflected light are polarized by passing through a quarter-wave plate; and A method for measuring a three-dimensional shape using a phase shift interferometer and an AFM, characterized by comprising a step of obtaining a plurality of interference images having different polarization states by interfering the first polarized reflected light and the second polarized reflected light polarized by a polarizing camera.

Images