JP4936541B2 - Atomic force microscope - Google Patents

Description

  The present invention relates to an atomic force microscope that is a scanning probe microscope using atomic force.

  The atomic force microscope scans a cantilever with a fine probe along the surface of the specimen, and the amount of displacement of the cantilever due to the atomic force acting between the probe and the specimen Is a device that can measure the fine structure of the surface of the test object. The principle is disclosed in Patent Document 1. In Patent Document 1, the amount of displacement of the cantilever is detected by detecting a tunnel current, but methods using an optical lever method or an optical interference method have also been proposed.

  However, the general atomic force microscope does not acquire displacement information of the test object when measuring the cantilever displacement. The same applies to the atomic force microscope disclosed in Patent Document 1. When the relative position between the cantilever and the test object fluctuates due to disturbance such as vibration or temperature change, the fluctuation amount is superimposed on the measurement result. There was a problem. For example, in the AC mode in which measurement is performed while the cantilever is vibrated in the vicinity of the resonance frequency, an atomic force that varies depending on the distance between the probe and the test object is detected by a change in amplitude. At this time, it is assumed that the distance between the probe and the test object changes according to the surface shape of the test object, but if the relative position fluctuation between the cantilever and the test object occurs, the assumption does not hold and the error is Will occur.

  Patent Document 2 has been proposed as an atomic force microscope capable of reducing the influence of relative position fluctuation between a cantilever and a test object. In Patent Document 2, the displacement amount of the cantilever is detected by an optical heterodyne method using an optical system including a bifocal lens, and the configuration thereof is as shown in FIG.

  In this apparatus, a laser light source apparatus 110 that can output laser light including two types of linearly polarized light having orthogonal polarization planes and slightly different frequencies is used. Two types of linearly polarized light output from the laser light source device 110 are incident on the bifocal lens 122, and one of the linearly polarized light becomes parallel light and is irradiated on a relatively wide range of the test object 130. The other linearly polarized light becomes focused light and is condensed on the back surface of the cantilever 126. The reflected light from the back surface of the cantilever and the reflected light from the surface of the test object enter the measurement optical sensor 136. Here, the reflected light from the back surface of the cantilever is subjected to a frequency change because the optical path length changes with the amount of displacement of the cantilever 126 due to the atomic force. Therefore, the displacement amount of the cantilever 126 can be calculated from the beat signal of the optical interference detected by the measurement optical sensor 136.

  When the measurement in the AC mode is applied to Patent Document 2, the maximum value and the minimum value of the cantilever displacement are measured with respect to the surface of the test object, and the amplitude is obtained. Therefore, even when the relative position fluctuation between the cantilever and the test object occurs, the maximum value and the minimum value of the cantilever displacement change equally by the relative position fluctuation, and the amplitude measurement result is not affected. For this reason, it becomes possible to reduce the influence of the relative position fluctuation | variation of a cantilever and a test object.

JP-A-62-130302 Japanese Patent No. 2998333

  However, in the case of the atomic force microscope disclosed in Patent Document 2, the influence of the relative position fluctuation between the cantilever and the test object can be reduced, but the test object is ideally aligned with the cantilever. Otherwise, the cantilever displacement cannot be measured. That is, the cantilever displacement can be measured only after the measurement is performed. For this reason, the measurement preparation work for performing adjustment while measuring the amount of cantilever displacement, such as cantilever mounting and cantilever touch-down operation, is hindered and has practical problems.

  The present invention has been made in order to solve the above-described problems. In an atomic force microscope that measures cantilever displacement using a test object as a measurement reference, an interatomic device capable of measuring cantilever displacement regardless of the state of the test object. An object is to provide a force microscope.

  In the atomic force microscope of the present invention, a cantilever having a probe is brought close to a test object, an atomic force generated between the probe and the test object is detected, and the atomic force is kept constant. In the atomic force microscope that measures the surface shape of the test object by scanning while scanning, the light source, the dividing unit that divides the light from the light source into first and second light beams, and the first A first optical system for detecting displacement of the cantilever from first interference fringes obtained by irradiating the object and the cantilever with a light beam and reflecting the light beam, respectively, a reference mirror, the first and A second optical system for detecting displacement of the cantilever from second interference fringes obtained by irradiating the second light beam to the cantilever and the reference mirror, respectively, and reflecting the cantilever and the reference mirror, respectively. Features and That.

  With the above configuration, it is possible to measure the cantilever displacement by the first optical system using the test object as a measurement standard and to measure the cantilever displacement by the second optical system using the reference mirror as a measurement standard. For this reason, even in the measurement preparation stage such as cantilever mounting and cantilever touchdown, the adjustment work can be performed using the measurement result of the cantilever displacement by the second optical system.

  In the first optical system, the optical path is divided by the polarizing optical element, and one of the polarized lights is irradiated onto the reflecting surface provided at the tip of the cantilever and the other polarized light is irradiated onto the surface of the test object. By combining this with a mechanism that rotates the wave plate and manipulates the polarization state of the light, a state in which the polarized light does not enter the specimen and the first light beam enters only the tip of the cantilever is created. Can do. Therefore, the cantilever displacement can be measured using the reference mirror as a measurement standard regardless of the presence or absence of the test object.

  Furthermore, by providing a mechanism that blocks the light (second light beam) incident on the reference mirror by the shutter, when measuring the cantilever displacement based on the test object, the shutter is closed to block the reflected light from the reference mirror. The generation of unnecessary interference fringes can be avoided.

  By selecting the light to be interfered by the wave plate rotation mechanism and the shutter in this way, it is possible to appropriately acquire cantilever displacement information according to the work contents, and it is possible to carry out from the preparation stage before measurement to actual measurement without delay. A simple atomic force microscope can be realized.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 shows a configuration of an atomic force microscope according to the first embodiment. This apparatus detects an atomic force generated between an atom of a needle-like probe and an atom on the surface of the test object 1 and performs scanning while keeping the atomic force constant. An XYZ stage 3 and a tip tilt stage 4 are provided on a base 2 that is fixed to the ground. A test object 1 is fixed to the tip tilt stage 4, and a housing 6 is fixed to the XYZ stage 3. Various optical components and sensors are built in the housing 6, and an XY scanner 7 is fixed as a fine movement mechanism in the XY directions. A tube scanner 8 is fixed to the XY scanner 7 as a fine movement mechanism in the Z direction. A cantilever 12 having the probe is attached to the tube scanner 8 via a cantilever unit attachment block 9, a piezoelectric actuator 10 for vibration, and a cantilever holder 11. A reflective surface is formed on the back surface of the tip of the cantilever 12.

  A measurement operation using the various drive mechanisms described above will be described. First, the test object 1 is fixed to the tip tilt stage 4, and the relative positional relationship between the test object 1 and the cantilever 12 is adjusted using the XYZ stage 3 and the tip tilt stage 4. Thereafter, the tube scanner 8 is used to bring the cantilever 12 closer to the test object 1 until an atomic force acts between the test object 1 and a probe (not shown) provided at the tip of the cantilever. The cantilever 12 is scanned using the XY scanner 7 while keeping the atomic force constant, and the surface shape of the surface of the test object 1 is measured. In order to keep the interatomic force constant, in this embodiment, the displacement of the tip of the cantilever is measured using optical interference. In this embodiment, the piezoelectric actuator 10 for vibration is provided, and measurement in the AC mode is also possible.

  Next, a first optical system (an optical system for measuring the surface shape) of the atomic force microscope in this embodiment and a method for measuring the cantilever tip displacement using this optical system will be described.

  The light output from the light source 21 is guided to the inside of the housing 6 through the optical fiber 22 and converted into parallel light by the collimator 23. The parallel light emitted at this time is adjusted to be linearly polarized light. Thereafter, the light (first light beam) transmitted through the half-wave plate 24 and the half mirror 26 is reflected by the dichroic mirror 27 and enters the lotion prism 28 which is a polarization optical element. The lotion prism 28 is made of a birefringent material (for example, calcite), and separates incident light into two types of orthogonally polarized light (S-polarized light and P-polarized light) and emits them in different directions. The S-polarized light is condensed by the condensing lens 29 onto the reflecting surface provided on the back surface of the cantilever 12 and is reflected at the vertex. Thereafter, the light enters the lotion prism 28 again through the same optical path as the incident optical path. On the other hand, the P-polarized light is condensed on the surface of the test object 1 and reflected at the apex. The reflected light enters the lotion prism 28 again through the same optical path. Both S-polarized light and P-polarized light transmitted through the lotion prism 28 pass through a common optical path as parallel light and are reflected by the dichroic mirror 27 and the half mirror 26. Then, the light passes through the quarter-wave plate 30, the half-wave plate 31, the half mirror 33, and the half mirror 34, and reaches the polarization beam splitter 35. The light is again split into S-polarized light and P-polarized light by the polarization beam splitter 35, and enters the photodetector 36 and the photodetector 37. The two photodetectors acquire light intensity information and transmit it to the arithmetic unit 38. The computing device 38 analyzes two types of intensity information and calculates the amount of cantilever displacement caused by the first interference fringes.

  The analysis contents in the arithmetic unit 38 will be described in further detail. If the optical information acquired by the photodetector 36 is A1, and the optical information acquired by the photodetector 37 is A2, the following information can be expressed.

ここで、Ａは光情報の大きさを定義する定数であり、λは使用している光の波長、ΔＬはカンチレバー１２と被検物１の間の相対的な変位情報、αはローションプリズム２８で分離したＳ偏光とＰ偏光の光路長差から決まる初期位相である。Ｖは位相変化に対する光情報変化の感度を表す感度係数であり、０以上１以下の値をとる。また、Φは２分の１波長板３１を回転させる回転機構３２の回転角度に応じて変化する位相である。

Here, A is a constant that defines the magnitude of the optical information, λ is the wavelength of the light being used, ΔL is the relative displacement information between the cantilever 12 and the test object 1, and α is the lotion prism 28. This is the initial phase determined from the optical path length difference between the S-polarized light and the P-polarized light separated by. V is a sensitivity coefficient representing the sensitivity of the optical information change with respect to the phase change, and takes a value from 0 to 1. Further, Φ is a phase that changes according to the rotation angle of the rotation mechanism 32 that rotates the half-wave plate 31.

  In the arithmetic unit 38, these two types of signals are processed as follows to obtain displacement information S.

ここでΦがαを打ち消すように２分の１波長板３１の回転角度を調整し、かつ、ΔＬは非常に微小量であるとすると、変位情報Ｓは次式のように近似できる。

If the rotation angle of the half-wave plate 31 is adjusted so that Φ cancels α, and ΔL is a very small amount, the displacement information S can be approximated by the following equation.

このようにして求められた変位情報Ｓを用いると、次式が得られる。

When the displacement information S obtained in this way is used, the following equation is obtained.

上式よりカンチレバー１２と被検物１との間の相対的な変位情報を得ることができる。上式に含まれる感度係数Ｖは、Ｓ偏光とＰ偏光の重ね具合の良し悪しにより変化する値である。干渉縞がいわゆる縞一色状態であり、かつ高コントラストであれば、干渉縞の感度係数Ｖは１に近づく。

From the above equation, relative displacement information between the cantilever 12 and the test object 1 can be obtained. The sensitivity coefficient V included in the above equation is a value that changes depending on whether the S-polarized light and the P-polarized light are superimposed. If the interference fringes are in a so-called fringe monochromatic state and have a high contrast, the sensitivity coefficient V of the interference fringes approaches 1.

  As will be described later, this embodiment includes an adjustment mechanism for bringing the interference fringe sensitivity coefficient V close to 1. However, for high-precision measurement, the interference fringe sensitivity coefficient V is accurately measured, It is desirable to calculate displacement information using it.

  In order to obtain an accurate value of the interference fringe sensitivity coefficient V, intensity information of the photodetector 36 is acquired while the half-wave plate 31 is rotated by the rotation mechanism 32. By rotating the half-wave plate 31, the phase α included in the following expression representing the intensity information changes.

位相Φの変化に伴って強度情報が強弱し、最小強度Ａｍｉｎと最大強度Ａｍａｘを知ることができる。最低強度Ａｍｉｎと最大強度Ａｍａｘの値を用いると、干渉縞の感度係数Ｖは次式で求めることができる。

As the phase Φ changes, the intensity information becomes stronger and the minimum intensity Amin and the maximum intensity Amax can be known. When the values of the minimum intensity Amin and the maximum intensity Amax are used, the interference fringe sensitivity coefficient V can be obtained by the following equation.

上式により求めた感度係数Ｖの実測値を用いて変位情報Ｓを計算することで、カンチレバー１２の変位を高精度に計測することができる。なお、感度係数Ｖの計測はフォトディテクタ３７より得られる強度情報により実施してもよい。

By calculating the displacement information S using the measured value of the sensitivity coefficient V obtained by the above equation, the displacement of the cantilever 12 can be measured with high accuracy. Note that the sensitivity coefficient V may be measured based on intensity information obtained from the photodetector 37.

  Next, various adjustment functions necessary for performing high-precision measurement will be described.

  In order to perform high-precision measurement in the present embodiment, it is desirable that the interference fringes detected by the photodetector 36 and the photodetector 37 are in a so-called fringe single color state. The interference fringes detected by the photodetector 37 are in a state where the phase is shifted by 180 degrees with respect to the interference fringes detected by the photodetector 36. Therefore, if one of the interference fringes is in a single color state, the other is also in a single color state.

  Therefore, in this embodiment, a CCD sensor 53 is provided as a sensor for adjusting the interference fringes to the one-color fringe state. Light that has been split by the half mirror 34, transmitted through the polarization beam splitter 51, and expanded by the beam expander 52 is incident on the CCD sensor 53. Accordingly, the interference fringes observed by the CCD sensor 53 are the same as the interference fringes detected by the photodetector 36. For this reason, by adjusting the tip tilt stage 4 so that the interference fringes observed by the CCD sensor 53 are in a striped color state, the interference fringes detected in the photo detector 36 and the photo detector 37 can be in a striped color state. .

  However, when the test object 1 is fixed with a large inclination, there is a possibility that the interference fringes cannot be observed in the CCD sensor 53. Therefore, in this embodiment, a position sensor 55 is provided. The light split by the half mirror 33 is incident on the position sensor 55. Therefore, the reflected light from the cantilever 12 and the reflected light from the test object 1 enter the position sensor 55. Then, the tip tilt stage 4 is adjusted so that two bright spots observed by the position sensor 55 overlap. Thereby, it can adjust so that the reflected light from the cantilever 12 and the reflected light from the to-be-tested object 1 may take a substantially common optical path. Therefore, the interference fringes can be observed in the CCD sensor 53, and the interference fringes can be adjusted to be in a single color state.

  In addition, the present embodiment includes a camera 56 and can observe the state of the tip of the cantilever. By using the camera 56, it is possible to adjust so that the light condensed by the condenser lens 29 is irradiated to a predetermined place on the back surface of the cantilever.

  Thus, by measuring the displacement of the cantilever using the test object 1 as a measurement reference, the influence of the relative position fluctuation between the cantilever 12 and the test object 1 can be reduced, but the test object 1 is ideally aligned. Otherwise, the cantilever displacement cannot be measured.

  In this embodiment, therefore, the reference mirror 63 for various adjustments is provided, and a second optical system for detecting the displacement of the cantilever 12 from the second interference fringe using the reference mirror 63 as a measurement standard is provided.

  The reference mirror 63 is reflected by the half mirror 26 that is a dividing means, separated from the light (first light beam) incident on the first optical system, and transmitted through the quarter-wave plate 61 and the shutter 62. Light (second light beam) is incident. The reflected light reflected by the reference mirror 63 passes through the shutter 62, the quarter-wave plate 61, and the half mirror 26, and reaches the photodetector 36 and the photodetector 37.

  Further, in this embodiment, a rotation mechanism 25 that can rotate the half-wave plate 24 around the optical axis is provided, and the polarization direction of the linearly polarized light emitted from the half-wave plate 24 can be freely set. Can be operated.

  Here, consider a case where the linearly polarized light emitted from the half-wave plate 24 is adjusted so as to be S-polarized light. At this time, all of the S-polarized light, which is the first light beam that passes through the half mirror 26 and reaches the lotion prism 28, enters the back surface of the cantilever 12 and does not enter the test object 1. Therefore, the light finally reaching the photo detector 36 and the photo detector 37 is only the reflected light from the cantilever 12. On the other hand, the light that is the second light beam reflected by the half mirror 26 is reflected by the reference mirror 63 and is incident on the half mirror 26 again. During this time, the light passes through the quarter-wave plate 61 twice and becomes P-polarized light. Is converted. Finally, the light reaches the photo detector 36 and the photo detector 37, and the arithmetic unit 38 calculates the optical path length difference using the second interference fringes. In this way, the cantilever displacement with the reference mirror 63 as a measurement standard can be detected.

  Next, consider a case where the linearly polarized light emitted from the half-wave plate 24 includes both an S-polarized component and a P-polarized component. At this time, in the light (first light beam) transmitted through the half mirror 26 and reaching the lotion prism 28, the S-polarized component is incident on the back surface of the cantilever 12, and the P-polarized component is incident on the test object 1. Incident. Then, the light reflected by the back surface of the cantilever 12 and the light reflected by the test object 1 reach the photodetector 36 and the photodetector 37. However, the light (second light beam) reflected by the half mirror 26 and reflected by the reference mirror 63 also reaches the photodetector 36 and the photodetector 37. Therefore, the three types of light interfere with each other in the photodetector 36 and the photodetector 37, and the optical path length difference cannot be calculated.

  Therefore, in this embodiment, a shutter 62 that is opened and closed by a driving unit is provided, and the optical path to the reference mirror 63 is shielded by closing the shutter 62. As a result, the reflected light from the reference mirror 63 does not reach the photo detector 36 and photo detector 37, and the displacement of the cantilever 12 relative to the test object 1 can be measured.

  An example of a cantilever touchdown sequence using the second optical system described above will be described with reference to the flowchart of FIG.

  When the touchdown command is issued (step S01), first, the shutter 62 is opened so that light enters the reference mirror 63 (step S02). Further, the half-wave plate 24 is rotated to change the polarization direction of linearly polarized light to S-polarized light (step S03). At this time, the photodetector 36 and the photodetector 37 detect interference fringes (second interference fringes) between the reflected light from the cantilever 12 and the reflected light from the reference mirror 63.

  Next, the half-wave plate 31 is rotated to make the displacement output zero, thereby canceling the initial phase (step S04). Further, by rotating the half-wave plate 31 (step S05), the sensitivity coefficient V of the photodetector 36 and the photodetector 37 with respect to the phase change is confirmed (step S06). Here, when the sensitivity coefficient V is low and the photodetector sensitivity to the cantilever displacement is insufficient, it is necessary to stop the touchdown process and adjust the cantilever 12 and the reference mirror 63 to ensure the sensitivity (step S07).

  When the sensitivity check is completed, the XYZ stage 3 is adjusted so that the cantilever 12 is disposed above the measurement point of the test object 1. Further, the tip tilt stage 4 is adjusted so that the principal ray of the polarized light condensed by the condenser lens 29 is perpendicularly incident on the test object 1. The adjustment at this time is performed based on the design value information of the test object 1 (step S08).

  When the stage position is adjusted, the Z-axis is lowered (step S09), and the cantilever 12 is touched down on the test object 1 (step S10). Whether or not the cantilever 12 is touched down can be determined by measuring the displacement of the cantilever 12.

  When the cantilever 12 is touched down, the configuration is changed to a configuration (first optical system) that measures the displacement of the cantilever 12 using the test object 1 as a measurement reference. That is, the shutter 62 is closed to block the reflected light from the reference mirror 63 (step S11), and the half-wave plate 24 is rotated so that both the P-polarized component and the S-polarized component are emitted (step S11). S12). At this time, it is desirable to determine the ratio of the P-polarized component and the S-polarized component according to the reflectance of the test object 1 and the cantilever 12. Specifically, it is desirable to adjust so that the amount of P-polarized light reflected by the test object 1 and the amount of S-polarized light reflected by the cantilever 12 are substantially equal. By adjusting in this way, the contrast of the interference fringes detected by the photodetector 36 and the photodetector 37 is increased, and highly accurate measurement can be performed.

  After changing the optical system of the measurement system, the position of the bright spot detected by the position sensor 55 is confirmed (step S13). Reflected light from the test object 1 and reflected light from the cantilever 12 are incident on the position sensor 55, and the interference fringes are detected by the photodetector 36 and the photodetector 37 if the positions of the two bright spots coincide. be able to. If the two bright spots do not match, the cantilever 12 is once detached from the test object 1 and the two bright spots are matched by adjusting the tilt of the test object 1 using the tip tilt stage 4 ( Step S19). After the adjustment, the shutter 62 is opened (step S20), and the half-wave plate 24 is rotated to convert the polarization direction of linearly polarized light into S-polarized light (step S21), and the cantilever 12 is measured using the reference mirror 63 as a measurement standard. The second optical system is used to measure the displacement of. Then, the position adjustment of the test object 1 is completed by touching down again.

  When the cantilever 12 touches down on the test object 1 and the positions of the two bright spots detected by the position sensor 55 coincide with each other, the half-wave plate 31 is rotated to set the displacement output to zero, thereby setting the initial phase. Cancel (step S14). Further, by rotating the half-wave plate 31, the sensitivity of the photodetector 36 and the photodetector 37 with respect to the phase change is confirmed (step S15). Here, when the sensitivity coefficient V is low and the photodetector sensitivity to the cantilever displacement is insufficient (step S16), it is necessary to stop the touchdown process (step S17) and adjust the test object 1 to ensure the sensitivity. . If the sensitivity is good, the touchdown process is completed (step S18), and the preparation for measuring the surface shape of the test object 1 is completed.

  According to the present embodiment, the cantilever displacement can be measured using the reference mirror as a measurement standard regardless of the presence or absence of the test object, and an atomic force microscope that can be carried out without delay from the preparation stage before measurement to actual measurement is realized. can do.

  In this embodiment, a lotion prism is used as the polarizing optical element, but the same effect can be obtained by using a Wollaston prism instead. In this embodiment, the S-polarized light is irradiated on the back surface of the cantilever and the P-polarized light is irradiated on the test object. However, the S-polarized light and the P-polarized light may be reversed. In this case, by making the linearly polarized light emitted from the half-wave plate 24 P-polarized light, it becomes possible to measure the cantilever displacement using the reference mirror 63 as a measurement standard.

  FIG. 3 is a diagram illustrating a configuration of an atomic force microscope according to the second embodiment. The difference from the first embodiment is that the positions of the quarter-wave plate 30 and the half-wave plate 31 and the position of the half mirror 33 are reversed, and further, between the half mirror 33 and the position sensor 55, The polarization beam splitter 54 is inserted. Only the reflected light from the test object 1 is incident on the position sensor 55 and the reflected light from the cantilever 12 is not incident. Then, the tip tilt stage 4 is adjusted using the positional information of one bright spot to be observed so that the interference fringes are in a single color state. That is, the ideal position of the bright spot where the interference fringes are in a single-colored state is known in advance, and the tip tilt stage 4 is adjusted so that the bright spot moves to the ideal position.

  The feature of the present embodiment is that the bright spot position can be calculated more accurately by calculation by a computer because there is only one bright spot detected by the position sensor 55. For this reason, the alignment state of the test object 1 can be obtained with high accuracy only by a computer, and this is a form suitable for automatic measurement.

  FIG. 4 is a diagram illustrating a configuration of an atomic force microscope according to the third embodiment. The difference from the first and second embodiments is that the number of interference fringe detection photodetectors is reduced to one. The analysis contents in the arithmetic unit 38 in this case will be described. Assuming that the optical information acquired by the photodetector 36 is A1, as described in the first embodiment, it is expressed by the following equation.

ここで、Ａは光情報の大きさを定義する定数であり、λは使用している光の波長、ΔＬはカンチレバー１２と被検物１の間の相対的な変位情報、αはローションプリズム２８で分離したＳ偏光とＰ偏光の光路長差から決まる初期位相である。Ｖは干渉縞の感度係数であり０以上１以下の値をとる。また、Φは２分の１波長板３１を回転させる回転機構３２の回転角度に応じて変化する位相である。

Here, A is a constant that defines the magnitude of the optical information, λ is the wavelength of the light being used, ΔL is the relative displacement information between the cantilever 12 and the test object 1, and α is the lotion prism 28. This is the initial phase determined from the optical path length difference between the S-polarized light and the P-polarized light separated by. V is a sensitivity coefficient of interference fringes and takes a value of 0 or more and 1 or less. Further, Φ is a phase that changes according to the rotation angle of the rotation mechanism 32 that rotates the half-wave plate 31.

  Here, if the rotation angle of the half-wave plate 31 is adjusted so that Φ cancels α, and ΔL is a very small amount, the optical information A1 can be approximated by the following equation.

このようにして求められた光情報Ａ１を用いると、次式が得られる。

When the optical information A1 thus obtained is used, the following equation is obtained.

上式より、カンチレバー１２と被検物１との間の相対的な変位情報を得ることができる。上式に含まれる光情報の大きさＡと干渉縞の感度係数Ｖは、２分の１波長板３１を回転機構３２により回転させながらフォトディテクタ３６の強度情報を取得し、最小強度Ａｍｉｎと最大強度Ａｍａｘを求めることで次式のように計算することができる。

From the above equation, relative displacement information between the cantilever 12 and the test object 1 can be obtained. The magnitude A of the optical information and the sensitivity coefficient V of the interference fringes included in the above formula are obtained by obtaining the intensity information of the photodetector 36 while rotating the half-wave plate 31 by the rotation mechanism 32, and the minimum intensity Amin and the maximum intensity. By calculating Amax, it can be calculated as follows.

なお、本実施例の場合、カンチレバー変位の符号がわからない欠点がある。しかしながら、カンチレバーの振幅情報を用いて計測を行なうＡＣモードではカンチレバー変位の符号情報を必要としないため、本実施例を適用することができる。

In the case of this embodiment, there is a drawback that the sign of the cantilever displacement is not known. However, in the AC mode in which measurement is performed using the amplitude information of the cantilever, the sign information of the cantilever displacement is not required, and thus this embodiment can be applied.

1 is a schematic diagram illustrating a configuration of an atomic force microscope according to Example 1. FIG. It is a flowchart explaining a cantilever touchdown process. 6 is a schematic diagram illustrating a configuration of an atomic force microscope according to Example 2. FIG. 6 is a schematic diagram illustrating a configuration of an atomic force microscope according to Example 3. FIG. It is a schematic diagram which shows one prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Test object 2 Base 3 XYZ stage 4 Tip tilt stage 6 Housing 7 XY scanner 8 Tube scanner 9 Cantilever mounting block 10 Excitation piezoelectric actuator 11 Cantilever holder 12 Cantilever 21 Light source 22 Optical fiber 23 Collimator 24 1/2 wavelength plate 25 Rotating mechanism 26 Half mirror 27 Dichroic mirror 28 Lotion prism 29 Condensing lens 30 Quarter wave plate 31 Half wave plate 32 Rotating mechanism 33 Half mirror 34 Half mirror 35 Polarizing beam splitter 36 Photo detector 37 Photo detector 51 Polarizing beam Splitter 52 Beam expander 53 CCD sensor 54 Polarizing beam splitter 55 Position sensor 56 Camera 61 Quarter wave plate 62 Shutter 63 Mirror

Claims (3)

A cantilever provided with a probe is brought close to the object to be detected, an atomic force generated between the probe and the object to be detected is detected, and scanning is performed while keeping the atomic force constant. In an atomic force microscope that measures the surface shape of an object,
A light source;
Splitting means for splitting light from the light source into first and second light beams;
A first optical system for detecting displacement of the cantilever from first interference fringes obtained by irradiating and reflecting the first light beam to the test object and the cantilever;
A reference mirror;
A second optical system for detecting displacement of the cantilever from second interference fringes obtained by irradiating the first and second light beams to the cantilever and the reference mirror, respectively, and reflecting them; An atomic force microscope characterized by comprising: A wave plate for changing the polarization direction of light from the light source;
A rotation mechanism for rotating the wave plate around the optical axis of the light;
A polarizing optical element that divides the first light beam into two types of polarized light,
The first optical system irradiates the cantilever with one of the two types of polarized light divided by the polarizing optical element, and condenses the other polarized light on the test object, and reflects each of them. The atomic force microscope according to claim 1, wherein the first interference fringes are obtained. A shutter for blocking the second light beam incident on the reference mirror;
The atomic force microscope according to claim 1, further comprising means for opening and closing the shutter.

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