Method for correcting film thickness of sample, method for calculating complex refractive index of sample

Abstract

Provided are a microscope system, a sample observation method, a sample film thickness correction method, and a sample complex refractive index calculation method. Troubles such as collision of a cantilever with a sample are suppressed. A microscope system (100) has a probe unit (40) having a cantilever (43), a camera (15), a camera position fine adjustment mechanism (17) that drives the camera in order to adjust the position of the camera with respect to a sample (S), and a computer (30) that controls the camera position fine adjustment mechanism to move the camera so that the focal point of the camera (15) is aligned with the back surface of the cantilever (43) or the surface of the sample. The computer calculates the distance (Δz) from the cantilever (43) to the surface of the sample (S) from the movement distance (Δz') of the camera (15) when the position of the camera is moved from the position at which the focal point of the camera (15) is aligned with the back surface of the cantilever (43) to the position at which the position of the camera (15) is aligned with the surface of the sample (S).

Description

TECHNICAL FIELD

[0001] The present application relates to a microscope system having a probe unit having a cantilever, and a sample observation method using the microscope system. BACKGROUND

[0002] Conventionally, in the field of sample observation, a microscope system combining an optical microscope and a scanning probe microscope (SPM) has been used. In such a microscope system, it is possible to efficiently perform observation of a sample by first observing a wide range of the sample by the optical microscope, and then observing a specific region in detail using the scanning probe microscope. Further, after approaching the sample at a distance estimated by focusing of the optical microscope, the scanning probe microscope is operated, whereby it is possible to quickly align the focus of the scanning probe microscope.

[0003] Patent Document 1 discloses a microscope system that measures the height of a sample by an optical microscope, corrects the scanning probe microscope based on the measurement result, and thereby measures the height of the sample with high precision by the scanning probe microscope.

[0004] Patent Document 2 discloses an atomic force microscope system having an observation system capable of optically observing a region of a cantilever and a sample, and a head system that causes light to be directed toward the cantilever, and obtains light reflected from the cantilever that shows movement of the cantilever.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2016-3919

[0006] Patent Document 2: Japanese Patent Application Publication No. 2012-506049

[0007] In the conventional apparatus, generally, the objective lens (bright field lens) of the optical microscope and the probe unit including the cantilever of the scanning probe microscope are mounted on a lens changer turret. The operator first aligns the focus of the optical system to the sample using the objective lens of the optical microscope, and obtains the 1st position of the sample based on the position of the objective lens at that time. Then, the operator switches the objective lens to the probe unit using the lens changer turret, and approaches the sample to the probe unit by an amount corresponding to the difference between the 1st position and the position of the cantilever of the probe unit, thereby aligning the position of the cantilever with the sample. By such an operation, it is possible to achieve detailed observation of the sample by the scanning probe microscope.

[0008] However, the value obtained by the above method is not always a correct value. In addition to this, there is a method of searching for a focal point position from an observation image of the probe unit. When the sample is a mirror surface and flat and there is no foreign matter as a marker around it, it is difficult to find the focal point. Also, the distance to the sample can slightly change depending on the mounting method of the cantilever. In these cases, it is possible that the cantilever collides with the sample because the probe unit is too close to the sample. SUMMARY

[0009] The present application provides a microscope system that can suppress the occurrence of a trouble such as a collision of a cantilever with a sample by being able to adjust the position of a camera.

[0010] The microscope system of the present application observes a sample, wherein the microscope system has: a probe unit having a cantilever that scans the surface of the sample; a camera that can be focused on the sample and the back surface of the cantilever; a drive section that drives the camera in order to adjust the position of the camera with respect to the sample; and a control section that controls the drive section, can move the camera to each of a position at which the focal point of the camera is aligned with the back surface of the cantilever and a position at which the focal point of the camera is aligned with the surface of the sample, and calculates the distance Δz from the cantilever to the surface of the sample from the movement distance Δz' of the camera when the position of the camera is moved from the position at which the focal point of the camera is aligned with the back surface of the cantilever to the position at which the focal point of the camera is aligned with the surface of the sample.

[0011] In the microscope system of the present application, for example, the control section controls the drive section so that the cantilever approaches the sample relatively in accordance with the calculated distance Δz.

[0012] In the microscope system of the present application, for example, the control section calculates a value smaller than the distance Δz by taking a prescribed margin value into account with respect to the distance Δz, and after controlling the drive section so that the cantilever approaches the sample relatively by an amount corresponding to this value, finely adjusts the distance between the cantilever and the sample.

[0013] In the microscope system of the present application, for example, the cantilever is an optical lever type, and the driving or displacement of the cantilever is detected by at least one laser. Alternatively, the cantilever can be a self-detection type, in which case a laser is not needed.

[0014] In the microscope system of the present application, for example, the probe unit is a lens type AFM unit that constitutes part of an Atomic Force Microscope (AFM).

[0015] In the microscope system of the present application, for example, the microscope system further has a turret in which the probe unit and at least one optical objective lens are capable of being mounted, and the turret is capable of switching the probe unit and the objective lens to each other to observe the sample.

[0016] In the microscope system of the present application, for example, when the probe unit is switched to the objective lens by the turret in order to observe the sample, the control section acquires the working distance of the objective lens, and calculates the distance by which the objective lens or the sample should be moved, based on the working distance and the position of the cantilever of the probe unit before the switching.

[0017] The present application is a method for observing a sample, in which a microscope system is used, the microscope system having a probe unit having a cantilever, wherein the method for observing a sample has the following steps: a step of aligning the focus of a camera with the back surface of the cantilever; a step of moving the camera so as to align the focus of the camera with the surface of the sample; and a step of calculating, by a computer, the distance Δz from the cantilever to the surface of the sample based on the distance Δz' of movement of the camera from the position at which the focus of the camera is aligned with the back surface of the cantilever to the position at which the focus of the camera is aligned with the surface of the sample.

[0018] The present application is a correction method, in a microscope system having a scanning probe microscope and an optical microscope, the scanning probe microscope having a probe unit having a cantilever that scans the surface of a sample, the optical microscope having an optical objective lens, wherein the measurement result of the film thickness of the sample by the optical microscope is corrected using a correlation between the measurement result of the film thickness of the sample by the scanning probe microscope and the measurement result of the film thickness of the sample by the optical microscope.

[0019] The present application is a calculation method, in a microscope system having a scanning probe microscope and an optical microscope, the scanning probe microscope having a probe unit having a cantilever that scans the surface of a sample, the optical microscope having an optical objective lens, wherein the complex refractive index of the sample is calculated using a correlation between the measurement result of the film thickness of the sample by the scanning probe microscope and the measurement result of the film thickness of the sample by the optical microscope.

[0020] Effects of the Invention

[0021] According to the microscope system of the present application, it is possible to suppress troubles such as collision of the cantilever with the sample by moving the position of the camera so that the focus is aligned with the surface of the sample. In addition, it is possible to shorten the time until the proximity is completed. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a whole configuration view of the microscope system as one embodiment of the present application.

[0023] Figure 2 is an enlarged view of the lens type AFM unit of the optical lever method.

[0024] Figure 3 is a conceptual view showing the imaging relationship of the lens in a general optical system.

[0025] Figure 4 is a graph showing the calculated value of the longitudinal magnification calculated from the magnification of the objective lens and the experimental value of the experiment.

[0026] Figure 5 is a conceptual view showing the proximity method based on the proximity of the lens type AFM unit to the sample, (a) shows the process of obtaining the 1st position of the sample using the bright field lens, (b) shows the process of calculating the distance Δz between the 1st position and the position of the cantilever of the lens type AFM unit, (c) shows the same process as (a), and (d) shows the process of making the sample approach the lens type AFM unit by the amount of distance Δz.

[0027] Figure 6 is a conceptual view showing the proximity method based on the proximity of the lens type AFM unit to the sample according to the present embodiment, (a) shows the process of recording the position of the camera when the focus of the camera is located at the back surface of the cantilever of the lens type AFM unit as the original position of the camera, (b) shows the process of moving the camera by the moving distance Δz' and aligning the focus of the camera with the surface of the sample, and (c) shows the process of making the sample approach the lens type AFM unit by the amount of distance Δz and aligning the focus with the sample.

[0028] Figure 7 is a flowchart showing the steps when the position adjustment of the camera in the microscope system according to the present embodiment is performed.

[0029] Figure 8 is a conceptual view explaining that the film thickness is measured to be thinner (due to measurement error and other errors) in the white color interferometry when the film thickness of the thin film is measured.

[0030] Figure 9 is a graph showing the measurement error that can occur in the white color interferometry due to the influence of the complex refractive index.

[0031] Figure 10 is a graph showing the relationship between the thickness of a thin film calculated by white interferometry and the thickness based on the AFM measurement, with the points plotted and an approximate curve shown.

[0032] Figure 11 is a flowchart showing the steps of correcting the result of height measurement based on white interferometry.

[0033] Figure 12 is a flowchart showing the steps for calculating the complex refractive index of a thin film.

[0034] Figure 13 is a flowchart showing the steps of moving the sample to an optimum position at the time of switching from the probe unit to the objective lens.

[0035] Explanation of Reference Numerals

[0036] 10: apparatus main body; 11: light source; 12: optical filter; 13: beam splitter; 14: objective lens; 15: camera; 16: lens changing turret; 17: camera position fine adjustment mechanism (driving section); 20: stage; 30: computer (control section); 40: probe unit; 41: XY detection element; 42: Z detection element; 43: cantilever; 44: built-in lens; 45: light position sensor; 100: microscope system; S: sample. DETAILED DESCRIPTION

[0037] Hereinafter, the embodiment of the microscope system of the present application will be described in detail using the drawings.

[0038] Figure 1 is a diagram showing the overall structure of the microscope system as one embodiment of the present application. The microscope system 100 includes an apparatus main body 10, a stage 20 on which a sample S (measurement object) as a measurement object is placed, and a computer (processor) 30 as a control section, which is responsible for the control of the microscope system 100 and processes the obtained data. The apparatus main body 10 includes a light source 11 such as a white light source for axial illumination, an optical filter 12 such as a wavelength filter provided as needed, a beam splitter 13, a camera (detector) 15 composed of, for example, an imaging element, and a camera position fine adjustment mechanism 17 as a driving section for driving the camera 15. In one example, the stage 20 is capable of moving in the xy direction as well as in the z direction.

[0039] Further, a lens changing turntable 16 is provided at the lower end of the device main body 10, which is driven manually by an operator or automatically by the computer 30. The lens changing turntable 16 is an adapter capable of mounting at least one lens, device, or the like, and one or more holes (not shown) capable of mounting various lenses, devices, or the like, are provided on the lower surface of the lens changing turntable 16. In this example, at least one optical objective lens 14 and a probe unit 40 are mounted on the lower surface of the lens changing turntable 16, and the probe unit 40 and the objective lens 14 can be switched to each other to observe a sample S. The objective lens 14 is a component that constitutes part of the function of an optical microscope in the microscope system 100, and is not particularly limited in kind to a bright field lens, an interference objective lens, or the like.

[0040] From the viewpoint of the function of the optical microscope, light from the light source 11 is reflected by the beam splitter 13 via the optical path of arrow A, and is emitted toward the sample S via the optical path of arrow B. The reflected light of the sample S returns again via the optical path of arrow B, reaches the camera 15, and is imaged. The optical microscope here is a concept that also includes a confocal microscope, an interferometer, or the like.

[0041] The probe unit 40 is a component that constitutes part of the function of a scanning probe microscope (SPM) in the microscope system 100. The probe unit 40 is, for example, a lens type AFM unit that constitutes part of an atomic force microscope (AFM) as one of scanning probe microscopes. Figure 1 The probe unit 40 in the microscope system 100 has, for example, an XY detection element 41 and a Z detection element 42 constituted by piezoelectric elements inside the housing thereof, and has a cantilever 43 on the lower surface. At the time of scanning, the probe (probe) of the cantilever 43 comes into contact with the surface of the sample S, the cantilever 43 is displaced up and down, and the XY detection element 41 and the Z detection element 42 detect the surface shape of the sample S by converting the displacement of the cantilever 43 into an electric signal. Figure 1 The probe unit 40 in the microscope system 100 is a so-called self-detection type unit, and the XY detection element 41 and the Z detection element 42 can directly detect the displacement of the cantilever 43.

[0042] Figure 2 The probe unit 40 in the microscope system 100 is a so-called self-detection type unit, and the XY detection element 41 and the Z detection element 42 can directly detect the displacement of the cantilever 43. Figure 1The probe unit 40 of the different light lever method has, in addition to the XY detection element 41, the Z detection element 42, and the cantilever 43, a built-in lens 44 and a light position sensor 45 (Position Sensitive Detector, PSD). At least one laser beam L emitted from a laser light source not shown is guided into the probe unit 40, is emitted to the back surface of the cantilever 43 through the built-in lens 44, is reflected by the back surface of the cantilever 43, and is guided to the light position sensor 45. Here, the XY detection element 41 and the Z detection element 42 control the deflection amount (drive or displacement) of the cantilever 43 regardless of the surface shape of the sample S so that the amount of the reflected laser beam L emitted to the center of the light position sensor 45 is constant. Thus, the surface shape of the sample S is detected by the displacement by the XY detection element 41 and the Z detection element 42 and the conversion of the displacement into an electric signal.

[0043] Since the objective lens 14 used in the optical microscope and the probe unit 40 used in the SPM are both present, the microscope system 100 of the present embodiment is of a configuration in which an optical microscope and an SPM are combined. That is, the microscope system 100 of the present embodiment can be used as an optical microscope using the objective lens 14 and as an SPM using the probe unit 40. Also, when used as two microscopes, the computer 30 controls the camera position fine adjustment mechanism 17 to move the position of the camera 15 so that the focal point of the camera 15 is aligned with the back surface of the cantilever 43 and the sample S, respectively, as indicated by an arrow F. Here, the emission of the laser beam L is kept in a state fixed to the back surface of the cantilever 43 and is not moved. The significance of this control will be described below. Figure 1

[0044] Figure 3 The imaging relationship of a lens in a general optical system is shown. The lateral magnification β, which corresponds to the so-called magnification of the objective lens and indicates the ratio of the size of the object to the size of the image, is found from the height y of the object (measuring target object), the height y' of the image of the object, the shooting distance z, the amount of feed z', the focal distance f to the objective lens, and the focal distance f' of the objective lens, by the following formula (1).

[0045] [Formula 1]

[0046]

[0047] In particular, in the case of a configuration in which an optical system called an infinite system is adopted, β0= f' / f holds.

[0048] ​On the other hand, the longitudinal magnification a orthogonal to the lateral magnification β is the ratio of the movement amount Δz' of the image along the optical axis direction to the movement amount Δz of the object along the optical axis direction, and is calculated by the following equation (2). The movement amount Δz of the object and the movement amount Δz' of the image are small compared to the size of the optical system.

[0049] [Equation 2]

[0050]

[0051] Further, when the magnification of the imaging lens (barrel lens) located on the opposite side of the objective lens is η0in the infinite system configuration, the following equation (3) holds according to equation (2) and the symmetry relation.

[0052] [Equation 3]

[0053]

[0054] The movement amount of the image until the alignment with the camera is Δz', which corresponds to the movement amount Δz' that the camera should be moved in order to focus the camera. By equation (3), the movement amount, i.e., the distance Δz, to the object can be calculated from the known movement amount Δz' of the position of the camera, the magnification of the objective lens, and the position of the camera when the focus is aligned with the back surface of the cantilever.

[0055] In addition, since the above equations (1) to (3) are based on the assumption condition (sin θ ≒ tan θ ≒ θ) that the paraxial ray holds, the paraxial ray does not hold as the magnification of the objective lens becomes high. However, the magnification of the objective lens used in the AFM is 20 times or less in general.

[0056] Figure 4 The calculated value of the longitudinal magnification calculated from the magnification of the objective lens and the experimental value based on the experiment are shown. According to this graph, in the case of the magnification of 20 times or less that is generally assumed, the deviation of the calculated value from the experimental value is small, and the condition that the paraxial ray holds is substantially satisfied.

[0057] Figure 5This conceptual illustration shows the operation of a conventional microscope system, similar to the microscope system 100 of this embodiment, capable of utilizing the functions of both an optical microscope and a lens-type AFM unit. In this system, a bright-field lens is used as the objective lens 14 in the optical microscope, and a lens-type AFM unit is used as the probe unit 40 in the scanning probe microscope. In such a microscope system, a large area of ​​the sample can be observed first using the optical microscope, and then a specific area can be observed in detail using the scanning probe microscope, enabling efficient sample observation. Furthermore, by estimating the approximate distance to the sample through focusing the optical microscope and approaching the sample at that distance, the scanning probe microscope can be operated, thereby quickly aligning its focus.

[0058] in particular, Figure 5 This conceptually illustrates the existing process of approaching and focusing on a sample based on a bright-field lens and a lens-type AFM unit. In existing microscope systems, the camera position fine-tuning mechanism 17, which serves as a drive unit in this embodiment, is not provided; the camera position is fixed.

[0059] exist Figure 5 In microscope systems, such as Figure 5 As shown in (a) and (c), the operator first uses the bright-field lens of the optical microscope to focus the optical system on the sample, obtaining the first position of the sample (the sample surface) based on the position of the bright-field lens at this time. Then, the operator uses the lens-changing turntable to switch the bright-field lens to a lens-type AFM unit. Since the position of the cantilever of the lens-type AFM unit is known, therefore... Figure 5 As shown in (b), the distance Δz between the first position and the cantilever position of the lens-type AFM unit can be determined. Therefore, as Figure 5 As shown in (d), the operator moves the sample (the surface of the sample) to the second position by bringing the sample closer to the lens-type AFM unit by a distance Δz, thus focusing the lens on the sample. This operation enables detailed observation of the sample using a scanning probe microscope. Furthermore, in this example, the sample is brought close to the lens-type AFM unit, but the lens-type AFM unit (and the main body of the device) can also be brought close to the sample.

[0060] However, the distance Δz between the first position of the specimen and the position of the lens-type AFM unit is not always an accurate value, for example, because it is estimated "based on the condition that the position of the cantilever will never change." Furthermore, there are methods to find the focal point of focus from the image observed by the probe unit. Also, the distance to the specimen can vary slightly depending on the cantilever's mounting method. In these cases, for example, problems may arise such as the cantilever colliding with the specimen if the probe unit is too close.

[0061] on the other hand, Figure 6 This diagram conceptually illustrates the process of a lens-type AFM unit approaching and focusing on a sample in the microscope system 100 of this embodiment. In this embodiment, a bright-field lens and a lens changing turntable are not used; instead, a camera 15 and a camera position fine-tuning mechanism 17, which serves as a drive unit for driving the camera 15, are used exclusively.

[0062] like Figure 6 As shown in (a), the operator first records the camera's position when the camera's focus is on the back of the cantilever of the lens-type AFM unit, using this position as the camera's origin. At this point, the sample (the sample's surface) is in position 1, but this is unrelated to the focus; the camera's focus is not aligned with the sample. The double-dotted line indicates the beam when the focus is aligned with the back of the cantilever. Then, as... Figure 6 As shown in (b), the operator operates the computer 30, which controls the camera position fine-tuning mechanism 17. The camera position fine-tuning mechanism 17 drives the camera 15 to move by a distance (movement amount) Δz', so that the focus of the camera 15 is aligned with the surface of the sample. The dashed line represents the light beam when the focus is aligned with the surface of the sample.

[0063] Since the distance Δz' the camera moves from the origin, the magnification β0 of the objective lens, and the magnification η0 of the imaging lens are known, the distance Δz to the sample can be calculated using equation (3). Therefore, as Figure 6 As shown in (c), the operator moves the sample (the sample surface) to position 2 by bringing the sample closer to the lens-type AFM unit by a distance Δz, thus aligning the focus on the sample. The double-dotted line indicates the beam when the focus is aligned with the back of the cantilever and the surface of the sample. This operation enables detailed observation of the sample using a scanning probe microscope. In this example, the sample is brought closer to the lens-type AFM unit, but the lens-type AFM unit (and the main body of the device) could also be brought closer to the sample. Furthermore, because the lateral magnification β changes slightly due to the movement of Δz', the size of the optical microscope image in the XY plane can be corrected.

[0064] Figure 7 This is a flowchart illustrating the steps involved in adjusting the position of the camera in the microscope system 100 performing this embodiment. First, it is determined that the cantilever 43 of the probe unit 40 is... Figure 1 Self-testing method, or Figure 2 The optical lever method (step S11). When the cantilever 43 is in the optical lever method, the operator adjusts the position of the built-in lens 44 so that the focus of the laser L is aligned with the back of the cantilever 43 (step S12).

[0065] The computer 30 records the position of the camera 15 when the focus is on the back of the cantilever 43 as the origin position (step S13). This corresponds to... Figure 6 The state of (a) is then determined. Then, through the operator's operation, the computer 30 controls the camera position fine-tuning mechanism 17, causing the camera position fine-tuning mechanism 17 to drive and move the camera 15 within its movable range (step S14). Furthermore, when the movable range of the camera is limited, sometimes the limit of the movable range is reached. When the limit of the movable range of the camera is reached ("Yes" in step S15), the operator moves the device body 10 containing the probe unit 40, causing the cantilever 43 to approach the sample S in a manner that does not collide with the sample S (step S16). Alternatively, the sample S can be moved towards the probe unit side. At this time, the camera 15 returns to its original position in a movable manner.

[0066] Computer 30 determines whether the focus of camera 15 has been aligned with the surface of sample S by moving camera 15 (step S17). When the focus of camera 15 is aligned with the surface of sample S by repeatedly performing steps S14 to S17 ( Figure 6 In state (b), the moving distance Δz' is calculated based on the difference between the position of camera 15 and the recorded origin position (step S18). Then, computer 30 calculates the distance Δz to the sample according to equation (3), and moves the worktable 20 carrying the sample S by the amount of distance Δz, shortening the distance between cantilever 43 and sample S, thus realizing... Figure 6 The state of (c) (step S19).

[0067] Furthermore, although theoretically, when the stage 20 is moved by a distance Δz, the cantilever 43 and the surface of the sample S will be aligned, in actual operation, to prevent a sudden collision, the stage 20 is first moved a distance smaller than the distance Δz (e.g., a value obtained by multiplying the distance Δz by a safety factor less than 1, or a value obtained by subtracting the value corresponding to the safety factor from the distance Δz) (a coarse adjustment). At this moment, the cantilever 43 and the surface of the sample S are, for example, close to about 100 μm, and then a fine adjustment is performed (as a fine adjustment of fine adjustment), thereby bringing the cantilever 43 and the surface of the sample S close to, for example, the nm level, where atomic force (AFM) can be detected. Fine adjustment can be achieved, for example, by using XY detection element 41, Z detection element 42, etc. In addition, in step S18, the device body 10 containing the probe unit 40 can also be moved closer to the sample S.

[0068] In the above process, the computer 30 as the control section performs the following processing in the above flow. The computer 30 controls the camera position fine adjustment mechanism 17 to move the camera 15 so that the focal point of the camera 15 is aligned with the back surface of the cantilever 43 and the surface of the sample S, respectively. Then, the computer 30 calculates the distance Δz from the cantilever 43 to the surface of the sample S from the moving distance Δz' of the camera 15 from the position at which the focal point of the camera 15 is aligned with the back surface of the cantilever 43 to the position at which the focal point of the camera 15 is aligned with the surface of the sample S. Then, the computer 30 calculates a value smaller than the distance Δz by a prescribed difference with respect to the distance Δz, and after the cantilever 43 is brought close to the sample S by an amount corresponding to the value by controlling the camera position fine adjustment mechanism 17, the distance between the cantilever 43 and the sample S is fine adjusted.

[0069] At the time of execution, the hardware (CPU or the like) of the computer 30 reads in a program that causes the above processing to be performed, and executes the sample observation method using the microscope system 100. Such a program is stored in the internal or externally provided storage device (hard disk, recording medium, memory, or the like) of the computer 30.

[0070] Further, in the above method, the camera 15 is used to perform the relative positioning between the cantilever 43 and the sample S. However, this camera 15 can also detect light from the objective lens 14 in the case where the sample S is observed through the objective lens 14. That is, in the case where the sample S is observed through the objective lens 14, the camera 15 can be used as a part of the optical microscope, that is, a photographing element, and the increase in the number of components can be suppressed. Figure 6 After the relative positioning between the cantilever 43 and the sample S as shown in the above, the objective lens 14 is brought into opposition to the sample S by driving the lens changing turret 16, and in this state, the camera 15 can function as a part of the optical microscope, that is, a photographing element, and the increase in the number of components can be suppressed.

[0071] In the above process, the computer 30 as the control section performs the following processing in the above flow. The computer 30 controls the camera position fine adjustment mechanism 17 to move the camera 15 so that the focal point of the camera 15 is aligned with the back surface of the cantilever 43 and the surface of the sample S, respectively. Then, the computer 30 calculates the distance Δz from the cantilever 43 to the surface of the sample S from the moving distance Δz' of the camera 15 from the position at which the focal point of the camera 15 is aligned with the back surface of the cantilever 43 to the position at which the focal point of the camera 15 is aligned with the surface of the sample S. Then, the computer 30 calculates a value smaller than the distance Δz by a prescribed difference with respect to the distance Δz, and after the cantilever 43 is brought close to the sample S by an amount corresponding to the value by controlling the camera position fine adjustment mechanism 17, the distance between the cantilever 43 and the sample S is fine adjusted. Figure 5 In the above conventional process, as described above, the distance Δz between the 1st position of the sample and the position of the lens type AFM unit is not always a correct value. Further, there is a method of searching for a focal point position in focus from an observation image of the probe unit. In the case where the sample is a mirror surface and is flat and there is no foreign matter around that becomes a mark, it is difficult to find the focal point. Also, the distance to the sample can slightly vary depending on the mounting method of the cantilever. In these cases, therefore, for example, there is a trouble that the cantilever collides with the sample because the probe unit is too close to the sample.

[0072] In the present embodiment, a bright field lens (objective lens) is not used in addition to the lens type AFM unit as the probe unit. Instead, in the present embodiment, the position of the camera is moved to align the focus on the surface of the sample. Since the cantilever does not approach the sample in the position adjustment of the camera, the cantilever can be prevented from colliding with the sample. Further, in the related art, since the coarse adjustment motor must be moved several times when the probe unit approaches the sample, the operation takes time in many cases, but according to the present embodiment, the time until the approach is completed can be shortened. Therefore, the safety is improved, and high-speed operation can be performed.

[0073] Further, in the related art, when the focus of the fixed camera is aligned on the back surface of the cantilever, the focus is not aligned on the surface of the sample. In particular, the small lens (small objective lens) assembled in the lens type AFM unit of the optical lever method is adjusted to irradiate the back surface of the cantilever, and thus cannot be moved. Therefore, another bright field lens (objective lens) is installed on the lens turret, and the approach is performed depending on the distance to the sample by the bright field lens, and thus the installation portion of the unit in the lens turret is necessarily occupied by the bright field lens. Further, the approach also takes time.

[0074] For the confocal microscope using the bright field lens, the problem does not become a particular problem, but for the white light interference microscope, the number of lenses that can be used is reduced, and the characteristics of the lens turret cannot be maximally utilized.

[0075] In the present embodiment, since the driving portion that can adjust the position of the camera is provided, the bright field lens is not necessary, and thus the cost can be reduced, and the objective lens (for example, an interference objective lens having different magnifications) having higher added value can be installed on the lens turret.

[0076] Further, the related art probe unit has a built-in coarse adjustment Z detection element as a piezoelectric element inside, and thus there is a tendency that the unit becomes significantly heavy. Further, there is a problem that the Z resolution in a small region is reduced by using a stacked piezoelectric element that increases the movable range.

[0077] In the present embodiment, the driving portion that can adjust the position of the camera is provided, and the lightweight of the probe unit can be achieved.

[0078] Further, in the related art, the lens turret is generally rotated, and thus there is a possibility that the center position of the field of view deviates by the amount of the mechanical tolerance corresponding to the concentric circles, but in the present embodiment, such a concern does not occur.

[0079] In addition, the piezoelectric elements such as the XY detection element 41 and the Z detection element 42 can be provided on the sample S side (stage 20), and can also be provided on the probe unit 40 side.

[0080] The probe unit 40 of the present embodiment is a unit that constitutes a part of a general scanning probe microscope (SPM), and in the present embodiment, a lens-type AFM unit that is one of scanning tunneling microscopes (STM). However, the probe unit 40 can also be applied to other scanning probe microscopes such as a magnetic force microscope (MFM), an electrostatic force microscope (EFM), and an atomic force microscope (AFM).

[0081] Next, a method of measuring the thickness of a metal film on a dielectric film using the microscope system 100 of the present embodiment will be described. As described above, the microscope system 100 of the present embodiment adopts a compound microscope that combines an optical microscope and an SPM. Measurement based on an optical microscope can be performed in a short time compared to an SPM, but in measurement using an optical microscope such as a white light interference microscope that performs height measurement using light (white light interference measurement), it has been known that the thickness of a metal film on a dielectric film is measured thinner than the actual thickness due to the complex refractive index of the metal.

[0082] As shown in FIG. 2, when light is normally incident from a medium having a refractive index n0 and an extinction coefficient k0 to a medium having a refractive index n1 and an extinction coefficient k1, the phase change due to reflection is given by the following formula. Figure 8

[0083] [Formula 4]

[0084]

[0085] Further, the phase difference between the light reflected from the sample 1 having the complex refractive index (n1, k1) and the light reflected from the sample 2 having the complex refractive index (n2, k2) is given by the following formula (5).

[0086] [Formula 5]

[0087]

[0088] Further, in a case where the extinction coefficient k1 of the sample 1 can be assumed to be 0, that is, in a case where the sample 1 is a dielectric (for example, a glass substrate), the following formula (6) holds.

[0089] [Formula 6]

[0090] ​

[0091] The thickness of the metal film deposited on the dielectric is measured to be smaller than the actual thickness due to the phase difference ΔΦ. The difference between the actual thickness and the measured thickness, i.e. the measurement error Δh, is obtained by the following equation (7).

[0092] [Formula 7]

[0093]

[0094] exist Figure 9 In this paper, when using a white interferometer as an optical microscope to measure the film thickness of the sample (sample 2), the calculation results of the resulting film thickness measurement error Δh are shown, assuming that the refractive index is n2, the extinction coefficient is k2, the imaginary part of the complex refractive index of the substrate glass (dielectric) is 0, and reflections from the back of the sample can be ignored (i.e., sample 1 is thicker). That is, in white interferometry, the smaller the refractive index n2, the larger the absolute value of the measurement error Δh, i.e., the greater the difference between the measured film thickness and the actual film thickness.

[0095] If the extinction coefficient k2 remains constant, the measurement error Δh is relatively easy to correct. However, the thinner the film, the greater the influence from various factors, such as back reflection. Furthermore, especially when measurements are performed using a white interference microscope, the measurement is not based on a single wavelength of the laser, so the extinction coefficient k2 for each wavelength is not necessarily fixed relative to the wavelength.

[0096] Figure 10 This is a graph obtained by plotting the film thickness measured by white interferometry (CSI) using a scanning white interferometer and the film thickness measured by a lens-type AFM unit (AFM-based measurement). The dashed line L10 is the ideal line when the measurement results in CSI and AFM are consistent, with a slope of 1. The solid line L11 is a solid line parallel to the dashed line L10 (with a slope of 1), with an intercept determined by equation (7), and with the ideal line L10 offset by the measurement error Δh, which is the intercept.

[0097] On the other hand, the one-dot chain line L12 is a line reflecting the actual state of the thin film, and since the slope is not 1, it does not deviate from the broken line L10 by an amount corresponding to the intercept as with the solid line L11. That is, although the measurement error Ah is not fixed, it is difficult to consider that the refractive index n2 of the thin film has changed, and thus according to the equations (4) to (7), it means that the extinction coefficient k2 changes depending on the thickness of the thin film. Such a change in the extinction coefficient k2 can be assumed to be linear or an exponential function (Lambert-Beer's law), and an approximate curve (fitting curve) obtained by approximation under such an assumption is the one-dot chain line L13. In the case of white light interferometric measurement, particularly thin film measurement, there is an influence of complex refractive index, back surface reflection, and the like, and a low-pass filter acts in the spatial direction at the diffraction limit, and the peak value decreases, and thus, it is shown that a result thinner than the measurement of the film thickness based on the AFM is measured.

[0098] Therefore, in reality, it is preferable to perform white light interferometric measurement and AFM measurement for each sample (the thickness of each sample is different), that is, for each sample in which the complex refractive index is different, and to obtain a correlation table (look-up table) in which correlation data indicating the correlation between them is summarized in a list, and then to perform height correction (film thickness correction). Figure 11 A step of correcting the result of height measurement based on white light interferometric measurement using the microscope system 100 of the present embodiment is shown.

[0099] First, the operator sets a sample in the microscope system 100 (step S21). In the case where the set sample is a new sample that has not been measured so far, and / or even in the case of a sample that has been measured, but there is no correlation data of the sample in terms of the height of the range of interest (correlation data of the thickness of the range of interest) (step S22; No), it is necessary to obtain the correlation data. Therefore, the operator operates the computer 30 of the microscope system 100 to perform height measurement (film thickness measurement) of the sample using the white light interferometric microscope and the lens-type AFM unit (step S23). The measurement based on the white light interferometric microscope is white light interferometric measurement using the objective lens 14, and the measurement based on the lens-type AFM unit is AFM measurement using the lens-type AFM unit as the probe unit 40 as in the above-described embodiment.

[0100] Further, the correlation relationship (correlation table) between the white light interferometric measurement and the AFM measurement is obtained from the measurement result of this height measurement, and specifically, the correlation relationship between the white light interferometric measurement and the AFM measurement is obtained from the measurement result of this height measurement, and specifically, Figure 10The approximate curve is shown (step S24). Through steps S23 and S24, the computer 30 corrects the result of the height measurement in the white light interferometry using the correlation relationship, excluding the influence of the complex refractive index and the like (step S25). The computer 30 pre-stores the correlation relationship in a memory, storage device, or the like, not shown, for each kind of sample after steps S23 and S24, whereby, when white light interferometry is performed on the same sample next time, the stored correlation relationship can be used to perform the correction, and the accurate film thickness can be calculated quickly. Of course, the correlation relationship can be obtained again by implementing steps S23 and S24 every time of observation.

[0101] That is, the height obtained optically can be corrected (calibrated) based on the value of the height obtained by the confocal microscope, the white light interference microscope, or the like (three-dimensional measurement microscope) and the result of the height obtained by the lens-type AFM unit. As described above, the AFM measurement is expected to be able to measure the film thickness with high accuracy without causing the measurement error Ah, compared to the measurement based on the optical microscope, but the measurement takes time compared to the measurement based on the optical microscope. Therefore, by the processing of Figure 11 , the correlation relationship between the AFM measurement and the optical microscope measurement is obtained for each sample in advance, and the measurement result of the optical microscope measurement is corrected based on the correlation relationship, whereby the relatively accurate film thickness can be obtained quickly.

[0102] The above is a correction method for correcting the measurement result of the film thickness of a sample based on an optical microscope in a microscope system having a scanning probe microscope having a probe unit having a cantilever that scans the surface of a sample and an optical microscope having an objective lens of an optical type. The film thickness of the sample can be measured by the scanning probe microscope and the optical microscope, the correlation relationship (for example, the correlation relationship described in Figure 10 ) between the measurement result of the film thickness of the scanning probe microscope and the measurement result of the film thickness of the optical microscope is obtained, and the measurement result of the film thickness of the optical microscope is corrected using the correlation relationship.

[0103] Further, in addition to the correction of the height, the complex refractive index (n2, k2) of the measurement sample can be found from the approximate curve of the measurement result of Figure 10 . Generally, n0, k0 are air, and n1, k1 are, for example, a glass substrate, and the like, for which k1 can be ignored. If the complex refractive index of the sample 2 is known, the fitting is easier, but even in the case where it is not known, the number of variables is two, n2, k2, and the complex refractive index of the measurement sample can be found from Figure 10The results of the experiment enable two lines, L11 and L12, which correspond to the equation, to be obtained, and thus the complex refractive index (n2, k2) can be calculated. However, it is to be noted that the manner in which the extinction coefficient k2 in the thin film changes is assumed to be linear or exponential.

[0104] Figure 12 The steps for calculating the complex refractive index of a thin film from the results obtained using the microscope system 100 of the embodiment are shown. First, the operator sets a sample in the microscope system 100 (step S31). Next, height measurement of the sample is performed by white interferometry and AFM measurement (step S32). Then, the correlation between the white interferometry and the AFM measurement, the approximation curve, is obtained from the measurement results of the height measurement (step S33). The complex refractive index (n2, k2) in the thin film is obtained from the measurement results and the approximation curve (step S34).

[0105] That is, the complex refractive index (n, k) of a thin film sample can be calculated from the value of the height obtained by an optical microscope (e.g., a confocal microscope, a white light interferometer, etc.) and the results of the height obtained by a lens-type AFM. The measurement results based on the measurement by the optical microscope can be used to quickly obtain the complex refractive index (n, k).

[0106] The above is a calculation method for calculating the complex refractive index of a sample in a microscope system having a scanning probe microscope having a probe unit having a cantilever that scans the surface of a sample and an optical microscope having an optical objective lens. The film thickness of the sample can be measured by the scanning probe microscope and the optical microscope, the correlation between the measurement results of the film thickness of the scanning probe microscope and the measurement results of the film thickness of the optical microscope (e.g., the correlation described in the above embodiment) is obtained, and the complex refractive index of the sample is calculated using the correlation. Figure 10 The above is a calculation method for calculating the complex refractive index of a sample in a microscope system having a scanning probe microscope having a probe unit having a cantilever that scans the surface of a sample and an optical microscope having an optical objective lens. The film thickness of the sample can be measured by the scanning probe microscope and the optical microscope, the correlation between the measurement results of the film thickness of the scanning probe microscope and the measurement results of the film thickness of the optical microscope (e.g., the correlation described in the above embodiment) is obtained, and the complex refractive index of the sample is calculated using the correlation.

[0107] In the dotted line L12 in the above, which reflects the actual state of the thin film, the measurement error Δh corresponding to the intercept decreases from around 32 nm in the AFM measurement to 0 nm. If the curve in which the refractive index n2 = 1.5 in the above is taken as an example, this phenomenon corresponds to the portion of the dotted line. As described above, since it is difficult to consider that the refractive index of the thin film changes, it can be assumed that the extinction coefficient k2 changes according to a linear or exponential function (Lambert-Beer's law), and the extinction coefficient k2 decreases as the measurement error Δh decreases. Furthermore, the complex refractive index (n2, k2) can be calculated from the correlation in the above, using the approximation curve. Figure 10 Figure 9 In the dotted line L12 in the above, which reflects the actual state of the thin film, the measurement error Δh corresponding to the intercept decreases from around 32 nm in the AFM measurement to 0 nm. If the curve in which the refractive index n2 = 1.5 in the above is taken as an example, this phenomenon corresponds to the portion of the dotted line. As described above, since it is difficult to consider that the refractive index of the thin film changes, it can be assumed that the extinction coefficient k2 changes according to a linear or exponential function (Lambert-Beer's law), and the extinction coefficient k2 decreases as the measurement error Δh decreases. Furthermore, the complex refractive index (n2, k2) can be calculated from the correlation in the above, using the approximation curve. Figure 10 Figure 9 The above is a calculation method for calculating the complex refractive index of a sample in a microscope system having a scanning probe microscope having a probe unit having a cantilever that scans the surface of a sample and an optical microscope having an optical objective lens. The film thickness of the sample can be measured by the scanning probe microscope and the optical microscope, the correlation between the measurement results of the film thickness of the scanning probe microscope and the measurement results of the film thickness of the optical microscope (e.g., the correlation described in the above embodiment) is obtained, and the complex refractive index of the sample is calculated using the correlation.​​

[0108] Next, problems that can occur when switching to the optical objective lens 14 using the lens changing turret 16 after performing SPM measurement using the probe unit 40 (for example, AFM measurement using a lens type AFM unit) and solutions thereof will be described. As described above, the microscope system 100 of the present embodiment adopts a composite machine of an optical microscope and an SPM. As a typical usage, a large area of a sample is observed by an optical microscope, and then a process of observing a specific area in detail using an SPM is performed, but conversely, cases where a large area of a sample is observed by an optical microscope again after a specific area is observed in detail using an SPM are also common, in which case, the lens changing turret 16 is driven to perform switching from the probe unit 40 to the objective lens 14.

[0109] The distance between the front end of the cantilever 43 of the probe unit 40 and the sample S is, for example, about 0.1 to 0.5 mm after approach by coarse adjustment, and reaches a small value of, for example, several angstroms to several nm or so at the time of fine adjustment (i.e., fine approach) measurement. On the other hand, in the case of observation using the objective lens 14, the working distance (WD) at the time of infinite configuration is given as a design value, and varies between several mm to several tens of mm depending on the lens. In addition, the WD refers to "the distance from the front end of the objective lens 14 to the sample surface", and the WD also changes in accordance with Formulas (1) to (3) due to the change in the camera position.

[0110] Thus, in measurement using the probe unit 40 and measurement using the objective lens 14, the distance with respect to the sample S adopts completely different ranges. Furthermore, when switching from the probe unit 40 to the objective lens 14, movement of the stage 20, the device main body 10 is also accompanied, and thus, cases where the image is blurred due to tolerance even if the same focus is mechanically maintained before switching often occur. In addition, the WD can differ depending on each lens. Therefore, in the case where the lens changing turret 16 is driven, the relative distance between the objective lens 14 and the sample must be determined in a manner consistent with the WD of each lens.

[0111] Therefore, in the microscope system 100 of the present embodiment, the following information is obtained in advance: the distance between the cantilever 43 and the sample S when the cantilever 43 is approached by moving the camera 15 up and down (i.e., the WD of the objective lens 14) and the distance between the cantilever 43 and the sample S when the cantilever 43 is approached by moving the stage 20 up and down (i.e., the WD of the objective lens 14). Figure 7the position of the sample S, and the WD of the objective lens 14 to be used next, i.e., the information of the optimal distance from the objective lens 14 to the sample S corresponding to the focusing. Then, the distance by which the sample S should be moved up and down at the time of switching to the objective lens 14 is calculated, and the position of the sample S is moved up and down by the distance including the calculated correction value. Note that the "sample position" here can be the absolute position of the sample S, or the relative position with a specific point (reference point) of the turret 16 as a reference. Thus, at the time of moving up and down the sample position, the sample S (the stage 20) can be moved, or the device main body 10 including the turret 16 and the like can be moved. By such processing, even when the turret is rotated, the relative distance between the objective lens 14 and the sample can be quickly and easily determined so as to coincide with the WD when the focal point is aligned with the sample S.

[0112] Figure 13 The step of moving the sample S to the optimal position at the time of switching from the probe unit 40 to the objective lens is shown. First, the computer 30 calculates the position of the current sample S in the microscope system 100 (step S41). Here, it is assumed that the measurement using the probe unit 40 has been performed. Next, the computer 30 determines whether the turret 16 is driven or not based on whether there is an input signal at the time of switching or not (step S42). In the case where the turret 16 is driven, the computer 30 acquires the WD of the objective lens 14 to be used after the switching (step S43). Then, the computer 30 calculates the distance by which the sample S should be moved based on the WD and the position of the cantilever 43 of the probe unit 40 before the switching (step S44), and drives the stage 20 to move the sample S (step S45). In steps S44 and S45, the distance by which the device main body 10 including the objective lens 14 and the turret 16 should approach the sample S can also be calculated and the approach can be performed. That is, the computer 30 calculates the distance by which the objective lens 14 or the sample S should be moved based on the WD of the objective lens 14 and the position of the cantilever 43 of the probe unit 40 before the switching.

[0113] It is preferable that which objective lens 14 or probe unit 40 is installed in which hole (mounting portion) of the turret 16 is known. However, the information on the mounting positions of the objective lenses 14 and the probe unit 40, their kinds, and the like can be input by the user each time.

[0114] The WD of each objective lens 14 (or the information from which the WD can be calculated) is preferably known. However, it can be input by the user each time.

[0115] Further, in Figure 13Before the step of the above-mentioned embodiment, it is necessary to obtain information on the position of the sample S at least once by moving the camera 15 up and down. Once the information is obtained, the current sample position can be calculated by adding or subtracting the distance by which the sample S is moved up and down thereafter. By obtaining the position information of the sample S in advance, the present method can be used not only at the time of switching from the probe unit 40 to the objective lens 14, but also at the time of switching from one objective lens to another objective lens.

[0116] In addition, the parfocal distance is standardized so that the image of the sample S does not become blurred even in the case of another lens in which the WD at the time of driving the lens turret 16 to switch to the infinity configuration is different. Therefore, at the time of switching the objective lens, the sample position is not originally required to be moved up and down. However, there are cases in which a device or a component that does not conform to the standard is used, or even if it conforms to the standard, the image of the sample S is blurred due to the influence of a tolerance or the like. Therefore, at the time of switching the objective lens, the sample position can also be moved up and down using the above-mentioned method.

[0117] Further, there are cases in which a driving device (motor or the like) that drives the lens turret 16 is provided. The driving device can automatically drive the lens turret 16 to change the used lens according to a driving instruction issued to the lens turret 16 by the user via an interface or an observation flow stored.

[0118] It is preferable to provide a sensor that detects the kind of the hole (provision portion) currently used in the lens turret 16, the used objective lens 14, or the probe unit 40, or a sensor that detects the driving of the lens turret 16 (particularly, manual-based driving). The timing at which the optimization of the WD should be started can be determined by the sensor. Further, the optimal WD calculation can also be automated by the sensor.

[0119] Further, the retraction processing of the sample S can also be performed to prevent collision before the driving of the lens turret 16. For example, the computer 30 issues a signal to the user to perform the retraction processing using a display or a speaker. In this case, in the calculation processing of the distance by which the sample position is moved up and down, the moving distance based on the retraction processing is considered.

[0120] Further, the processing of moving the position of the camera 15 up and down to a position suitable for bright field observation can also be performed at any timing after the kind of the used objective lens 14 is determined.

[0121] In addition, the present application is not limited to the above-mentioned embodiments, and can be appropriately deformed, modified, or the like. In addition, the material, shape, size, value, method, number, arrangement position, and the like of each constituent element of the above-mentioned embodiments are arbitrary as long as the present application can be achieved, and are not limited.

[0122] Industrial applicability

[0123] According to the microscope system of the present application, a microscope system capable of suppressing troubles such as collision of a cantilever with a sample, improving safety, and performing high-speed operation can be provided.

Claims

1. A film thickness correction method of a sample, in a microscope system having a scanning probe microscope and an optical microscope, the scanning probe microscope having a probe unit having a cantilever that scans a surface of a sample, the optical microscope having an objective lens of an optical type, wherein a measurement result of a film thickness of the sample by the optical microscope is corrected, the film thickness of the sample is measured by the scanning probe microscope and the optical microscope, a correlation between the measurement result of the film thickness of the sample by the scanning probe microscope and the measurement result of the film thickness of the sample by the optical microscope is obtained, and the measurement result of the film thickness of the sample by the optical microscope is corrected using the correlation.

2. A complex refractive index calculation method of a sample, in a microscope system having a scanning probe microscope and an optical microscope, the scanning probe microscope having a probe unit having a cantilever that scans a surface of a sample, the optical microscope having an objective lens of an optical type, wherein a complex refractive index of the sample is calculated, the film thickness of the sample is measured by the scanning probe microscope and the optical microscope, a correlation between the measurement result of the film thickness of the sample by the scanning probe microscope and the measurement result of the film thickness of the sample by the optical microscope is obtained, and the complex refractive index of the sample is calculated using the correlation. ​ ​ ​ ​ ​ ​

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