JPH08178933A - Surface measuring device - Google Patents

Abstract

PURPOSE: To measure the surface having elastic properties or viscosity of a sample by accurately detecting the force acting between a probe and the sample. CONSTITUTION: The surface measuring device has a probe 3 supported by a spring member 2 fixed at its one end and a displacement sensor 4 detecting the displacement of the probe 3 and is constituted so that the surface of a sample 1 is inspected by the probe 3 and the displacement of the probe 3 is detected by the displacement sensor 4 to measure the surface state of the sample 1. Further, a vibration element 5 exciting the spring member 2, an oscillator 6 vibrating the vibration element 5, a signal processing circuit 12 processing the output of the displacement sensor 4 to detect the vibration amplitude or phase thereof and recorders 14, 15 recording and displaying the output of the signal processing circuit 12 are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning probe microscope such as an atomic force microscope, and more specifically, measuring the surface condition of a sample from the physical quantity received from the sample by bringing a probe close to or in contact with the sample surface. To a surface measuring instrument.

[0002]

2. Description of the Related Art Conventionally, a probe is brought close to the surface of a sample,
As a scanning probe microscope for measuring the surface condition of a sample from the physical quantity received from the sample, JP-A-62-130302
An atomic force microscope disclosed in Japanese Patent Publication is disclosed. FIG. 7 shows this atomic force microscope. The main structure of this atomic force microscope is composed of a rigid base 101 made of, for example, an aluminum block. The arm 102 of the base 101 is XY
Mounted on the Z drive 103, this allows the sample 104 to be displaced in the X, Y and Z directions with respect to the stationary cusp 105. The cusp 105 is the base 1
The arm 1 that projects from 01 and supports the cantilever 107
It is supported on 06. In the preferred embodiment, the cantilever 107 is in the form of a leaf spring and the cusps 105 are the spring 10.
It is fixed to the upper end of 7.

A tunneling tip 108 faces the back of the spring 107, and the tip 108 is supported by a Z drive device 109 that advances and retracts relative to the spring 107. The Z drive device 109 is fixed to an arm 110 protruding from the base 101. This device needs to provide a device that eliminates all ambient vibrations such as building vibrations. This vibration is removed by the arm 10 of the base 101.
This can be achieved in part by the cushions 111, 112 of Viton rubber separating the drives 103 and 109 from 2 and 110.

In operation, sample 1 to be tested
No. 04 has a cusp 105 on its surface on the XYZ driving device 103.
It is installed so that it faces each other. Sample 104 has cusp 1
When the electron cloud of the atom at the apex of the cusp 105 approaches the distance of 05 to the distance of contacting the electron cloud of the atom on the surface of the sample 104, an interatomic force is generated. These repulsive forces are of the order of 10 ⁻¹² N, which causes the spring with the cusps 105 to flex.

The deflection of the spring 107 is measured by a fixed tunnel microscope. The spring 107 supports the arm 106 via the piezoelectric element 113. The tunneling tip 108 is moved toward the gold spring 107 by the Z drive device 109 within a tunneling distance, that is, within about 0.3 nm, and a tunnel current is passed between the spring 107 and the tip 108. At this time, it is assumed that an appropriate potential difference exists between them. This tunnel current is an exponential function of the distance between the tunnel electrodes. Therefore, the tunnel current can be used to derive the surface height of the actual inspection location from a constant or home level.

This atomic force microscope is used in its normal operation to map most of the surface, for example most of the surface of a semiconductor wafer or circuit board. Thus, the cusps 105 are scanned in a matrix across the sample. Plotting the tunneling current values for each spot on the surface of the sample against the location of that spot yields a topographical image on the surface of the sample. The change in tunneling current resulting from the scanning of the (usually non-planar) surface is used to generate the correction signal. This correction signal is fed back to the Z of the XYZ driving device 103 by a feedback loop.
Applied to the part to control the distance between the cusp 105 and the sample 104 to maintain the atomic force at a constant value. This atomic force microscope allows the formation of images of the surface with atomic resolution without the need for high energy or preparatory metal coatings.

[0007]

However, in the atomic force microscope according to the above-mentioned conventional technique, for example, when the sample surface is soft, such as when measuring the surface of a biological sample placed in a solution, a space between the probe and the sample surface is used. The force acting on the surface is determined by the elastic and viscous forces in the vicinity of the surface, so the force acting between the probe and the sample becomes unstable due to the time constant due to the elastic and viscous properties of the surface, making accurate surface measurement impossible. There was a problem.

The present invention has been made in view of the above conventional problems, and an object of the invention according to claim 1, 2, 3 or 4 is to provide a sample having at least a surface having elastic properties or viscosity. Another object of the present invention is to provide a surface measuring instrument capable of accurately detecting the force acting between the probe and the sample and measuring the surface.

[0009]

In order to solve the above problems, the invention according to claim 1, 2, 3 or 4 discloses a probe supported by a spring member having one end fixed, and a displacement of the probe. And a displacement sensor for detecting the surface of the sample with the probe, the displacement is detected by the displacement sensor, in the surface measuring instrument for measuring the surface state of the sample, the spring member is excited. A vibrating element, an oscillator that vibrates the vibrating element at a plurality of frequencies, a signal processing circuit that processes the output of the displacement sensor and detects the vibration amplitude or phase thereof, and records and displays the output of the signal processing circuit. A recorder is provided.

[0010]

The operation of the invention according to claim 1, 2, 3 or 4 is as follows. By vibrating the spring member at multiple frequencies, the output at the same measurement point at each frequency is detected, and the signal processing circuit calculates the output gradient between the frequencies to determine the elastic force or viscosity at that measurement point. taking measurement. An elastic force or viscosity distribution is obtained by scanning the entire surface of the sample. In the operation of the invention according to claim 2, in addition to the above operation, the processing speed is increased by the vibration due to the single pulse wave.
In the operation of the invention according to claim 3, in addition to the above operation, the oscillation frequency of the oscillator is controlled so that the output of the signal processing circuit becomes a predetermined instruction value, and the output corresponding to the surface elasticity or viscosity of the sample is generated. Can be detected. In the operation of the invention according to claim 4, in addition to the above operation, the sample is controlled in the Z direction so that the output of the signal processing circuit becomes a predetermined instruction value, and the sample corresponding to the predetermined surface elasticity and viscosity values. The height of the surface of can be detected.

[0011]

Example 1 FIGS. 1 and 2 show Example 1, FIG. 1 is a block diagram of a surface measuring device, and FIG. 2 is a table showing elastic curves of a sample surface.

In FIG. 1, reference numeral 40 denotes a base, which supports the displacement sensor 4, the vibration element 5, and the Z adjusting mechanism 11, respectively. The Z adjustment mechanism 11 is composed of a ball screw and a stage guide, and finely moves the XY scanner 10 and the sample 1 in the Z direction. The XY scanner 10 holds the sample 1 and can be finely moved in the X and Y directions, and is composed of a tube scanner using a piezoelectric element as a material or a laminated PZT formed in a tripot shape. The probe 3 is arranged so as to face the surface of the sample 1, and the probe 3 is fixed to one end of the spring member 2. The other end of the spring member 2 is held by the vibrating element 5. The spring member 2 is formed of an elastic member such as a thin piece of phosphor bronze having a thickness of several μm to several hundred μm. The probe 3 processes the tip of diamond to sharpen it and fixes it to the spring member 2 with an adhesive or the like. Further, the probe 3 and the spring member 2 may be integrally formed by a semiconductor manufacturing process. The vibrating element 5 is composed of a finely movable piezoelectric element, and is excited by a plurality of frequencies from the oscillator 6.

The displacement sensor 4 is arranged above the probe 3 at a position where the displacement of the probe 3 can be measured, and uses a commercially available optical displacement sensor, optical lever sensor, capacitance displacement sensor or critical angle sensor. The oscillator 6 is composed of a variable frequency sine wave oscillator, and is connected to the computer 14 so as to change the frequency according to a command from the computer 14. The computer 14 receives the XY scanner 1 via the D / A converter 22.
The sample 1 is slightly moved by driving 0 in the X and Y directions. The output of the displacement sensor 4 is, after detecting the effective value by the effective value circuit 12,
They are connected to each other so that they are input to the A / D converter 13, converted from analog to digital, and input to the computer 14. This input signal is sent to the computer 14
And is configured to be output to the display unit 15.

Next, the operation of this embodiment will be described. Sample 1 is an elastic body having a soft surface. The oscillator 6 is oscillated by the output from the computer 14, and the probe 3 is excited by the vibrating element 5. In this state, when the sample 1 is brought closer to the probe 3 by the Z adjustment mechanism 11, a physical force acts between the surface of the sample 1 and the tip of the probe 3. Figure 2 in this state
In order to obtain the elastic curve shown in (1), the oscillation frequency of the oscillator 6 is changed and the displacement sensor 4 measures the vibration displacement state of the probe 3. The displacement of the vibration is such that the vibration amplitude changes due to the physical force acting on the surface of the sample 1 and the tip of the probe 3, particularly the surface elastic force. In order to detect this, the effective value circuit 12 calculates the effective value of the output of the displacement sensor 4, and the A / D converter 1
The analog quantity is converted into a digital quantity by 3, and is stored in the computer 14. Next, a command is given by the computer 14, and the XY scanner 10 is finely moved in the X and Y directions, and the sample 1
By slightly moving, the measurement point is moved, and the elasticity curve is stored in the computer 14. This operation is sequentially repeated to store data on the entire surface of the sample. From the stored data, the frequencies fc and f shown in FIG.
The gradient of the output between b and the frequency fcfb is processed by the computer 14, and the elasticity distribution on the sample surface is displayed on the display 15 as a two-dimensional image.

Now, the elastic curve of FIG. 2 will be described. The horizontal axis represents the oscillation frequency of the oscillator 6, and the vertical axis represents the vibration amplitude that is the output of the effective value circuit 12 that is the signal processing circuit. On the low frequency side, the vibration amplitude of the spring member 2 matches the amplitude of the vibrating element 5 because it is not affected by the elasticity of the surface of the sample 1. However, as the frequency is increased, the vibration amplitude of the sample 1 becomes closer to the frequency fc. The amplitude gradually decreases under the influence of the surface elasticity of, and the vibration amplitude approaches zero near the frequency fb. The elastic force at the measurement site is detected by the gradient of the output between the frequencies fc, fb and fcfb.

According to this embodiment, the elastic force of the surface of an elastic sample such as a biological sample can be detected. Further, since the XY scanner is equipped, the sample surface can be scanned and the two-dimensional elastic distribution can be observed.

In this embodiment, the elastic sample is used for explanation. However, even if the sample has a surface viscosity, the force acting on the probe 3 is the same and the surface viscosity distribution of this example is also the same. It can be observed with a surface measuring instrument.

Further, instead of the oscillator 6 of this embodiment, an oscillator having a pulsed output having a wide range of frequency components is used, and the output from the displacement sensor 4 is a waveform analysis device such as a lock-in amplifier or an FFT analyzer. The two-dimensional elastic distribution can also be observed by detecting with.

[0019]

[Embodiment 2] FIGS. 3 to 4 show Embodiment 2, FIG. 3 is a configuration diagram of a surface measuring device, and FIG. 4 is a table showing elastic curves of a sample surface. The configuration of the present embodiment is characterized in that a combination of the displacement sensor 4 and the spring member 2 in the first embodiment is used, and other parts are the same as those in the first embodiment. Are denoted by the same reference numerals and description thereof will be omitted.

In FIG. 3, reference numeral 31 is a composite spring member, which is formed by forming a piezoresistor on the upper surface of an elastic member such as a thin piece of phosphor bronze by using a semiconductor process. The piezoresistor is connected to the effective value circuit 12.
The probe 3 is fixed to the tip of the composite spring member 31, and the other end is held by the vibrating element 5. Since the base 41 does not require a displacement sensor, it is formed in a shape in which the holding portion of the displacement sensor of the first embodiment is missing. Other configurations are similar to those of the first embodiment.

The operation of this embodiment will be described. Sample 1
Is an elastic body similar to that of the first embodiment. Compound spring member 31
Bends due to a physical force acting between the surface of the sample 1 and the tip of the probe 3, and distorts the piezoresistor formed on the upper surface of the composite spring member 31. Due to this strain, the resistance value of the piezoresistor changes, and the amount of change is detected by a bridge circuit or the like to detect the amount of bending of the composite spring member 31. This amount of bending is zero when no force is applied from the surface of the sample 1, so that when the force begins to act, the elastic curve increases the output vibration amplitude as the vibration frequency increases as shown in FIG. . The frequencies fc, fb at this time,
The elastic force is detected by obtaining the gradient of the output between and ffcb, and the surface elastic distribution is observed.

According to the present embodiment, in addition to the effects of the first embodiment, the displacement sensor can be downsized, the structure of the entire device can be simplified, the rigidity of the device can be improved, and the influence of external vibration can be reduced. The measurement accuracy can be improved.

Also in the present embodiment, the elastic sample is used for explanation, but the modification shown in the first embodiment can be applied to the present embodiment. Further, since the vibration frequency of the vibrator 5 can be improved to several MHz, it is possible to measure with high sensitivity even a sample having a lower viscosity.

[0024]

Third Embodiment FIG. 5 shows a third embodiment and is a configuration diagram of a surface measuring instrument. In the configuration of this embodiment, only the control circuit is used in the first embodiment.
Since other parts are the same as those in the first embodiment, the same members are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 5, the output of the displacement sensor 4 is amplitude-detected by the absolute value circuit 17 including an operational amplifier and a diode, and is connected to the differential amplifier 18 so as to be input to the differential amplifier 18. The differential amplifier 18 makes a difference between the output signal of the absolute value circuit 17 and the output signal of the A / D converter 20 which changes with the output of the computer 14,
The PID control circuit 19 is connected so as to be input. P
The output of the ID control circuit 19 is connected so as to be input to the oscillator 6 and the A / D converter 13. The PID circuit 19 is a general feedback circuit and is composed of a proportional, integral and differentiating circuit. The other circuit configuration is the same as that of the first embodiment.

The operation of this embodiment will be described. Sample 1
Is an elastic body similar to that of the first embodiment. The vibration signal of the probe 3 detected by the displacement sensor 4 has its amplitude signal detected by the absolute value circuit 17, and is input to the differential amplifier 18. The differential amplifier 18 compares the servo instruction value output from the computer 14 with the signal of the absolute value circuit 17, and changes the oscillation frequency of the oscillator 6 by the PID control circuit 19 so that this value becomes zero. Feedback control is performed on the vibration element 5. As a result, the oscillation frequency of the oscillator 6 vibrates at a frequency corresponding to the physical force acting on the surface of the sample 1 and the tip of the probe 3, and the PID having a value corresponding to this frequency.
The output of the control circuit 19 is supplied to the sample 1 by the XY scanner 10.
The surface of is scanned, taken in by the computer 14, and displayed on the display 15, so that the elastic distribution is observed.

According to this embodiment, in addition to the effect of the first embodiment, the oscillation frequency of the oscillator is changed by the signal of the displacement sensor,
By feeding back, it is not necessary to change the oscillation frequency of the oscillator for each measurement point, so that the measurement speed can be increased.

Also in this embodiment, the elastic sample is used for explanation, but the modification shown in Embodiment 1 can be applied to this embodiment.

[0029]

[Embodiment 4] FIG. 6 shows Embodiment 4 and is a configuration diagram of a surface measuring instrument. The configuration of the present embodiment is different from that of the first embodiment only in the sample mounting portion and the control circuit, and the other parts are the same as those of the first embodiment. Therefore, the same members are designated by the same reference numerals and the description thereof will be omitted.

First, the structure of the sample mounting portion will be described. A scanner 26 composed of a tube scanner made of a piezoelectric material is supported by the Z adjustment mechanism 11 and holds a petri dish 27. The dish 27 is filled with a liquid 28 such as salt water, and the sample 1 is placed in this liquid. The probe 3 and the spring member 2 are submerged in the liquid 28 and approach the sample 1. Also,
The tip of the displacement sensor 4 is also submerged in the liquid 28. Other configurations are similar to those of the first embodiment.

Next, the structure of the control circuit will be described. The output from the displacement sensor 4 is amplitude-detected by an absolute value circuit 17 including an operational amplifier and a diode, and is connected to each other so as to be input to a differential amplifier 18. The differential amplifier 18 uses the absolute value circuit 17
Output signal and A / that changes depending on the output to the computer 14
The output signal of the D converter 20 is connected to the PID control circuit 19 so as to be different from the output signal. The output of the PID control circuit 19 is the scanner 26 and the A / D converter 1
3 is connected to input. The material 1 is slightly moved in the Z direction by inputting to the scanner 26. PID control circuit 1
Reference numeral 9 is a general feedback circuit, which is composed of a proportional, integral, and derivative circuit. The other circuit configuration is the same as that of the third embodiment.

The operation of this embodiment will be described. Sample 5
1 is a biological sample. The sample 51 is measured in a solution in order to bring the surface condition closer to the actual condition. Therefore, in this example, the sample 51 was submerged in the solution by the dish 27 and the solution 28. The computer 14 causes an oscillator 29
The oscillation frequency of is oscillated at a desired frequency to excite the probe 3. When the sample 51 is moved closer to the probe 3 by the Z adjustment mechanism 11, the amplitude of the vibration signal of the probe 3 changes. This amplitude change is detected by the absolute value circuit 17 and input to the differential amplifier 18. The differential amplifier 18 compares the signals of the absolute value circuit 17 with the servo instruction value output from the computer 14, and sets the PID so that this value becomes zero.
The scanner 26 is finely moved in the Z direction by the control circuit 19, and feedback control is performed so that the force acting between the surface of the sample 51 and the tip of the probe 3 is constant.

As a result, the control of the scanner 26 in the Z direction matches the output of the absolute value circuit 17 which detects the force acting between the sample 51 and the probe 3 with the servo instruction value in the previous period.
At the same time, the surface of the sample 51 is scanned by the scanner 26, and the output of the PID control circuit 19 is captured by the computer 14 and displayed on the display unit 15. Therefore, even if the surface of the sample 51 has a three-dimensional shape with large irregularities, The three-dimensional distribution of the surface shape corresponding to the elasticity and viscosity of the sample surface can be observed. The oscillation frequency of the oscillator 29 is determined to the desired frequency and the servo instruction value by using the elastic curve of FIG. 2 as described in the first embodiment.

According to this example, in addition to the effect of Example 1, by performing measurement while the sample was placed in the solution,
The sample can be measured in a measurement environment close to the actual one. In addition, by slightly moving the sample in the Z direction by the signal of the displacement sensor,
It is possible to observe a three-dimensional distribution of surface shapes corresponding to desired elasticity and viscosity values.

[0035]

According to the invention according to claim 1, 2, 3 or 4, the force acting on the surface of the sample and the tip of the probe can be accurately detected, even in the case of a sample having a large surface elasticity or viscosity. Various surface measurements can be performed. Claim 2
According to the invention of claim 1, in addition to the above effects, since the probe is operated in a pulsed manner to perform measurement, the surface elasticity and the viscosity characteristic can be detected at high speed. According to the invention of claim 3, in addition to the above effects, it is possible to constantly detect the output corresponding to at least the surface elasticity or the viscosity of the measurement point.
According to the invention of claim 4, in addition to the above effects, the height having a desired surface elasticity and viscosity can be detected, and the surface shape of the sample can be observed.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a surface measuring instrument according to a first embodiment.

FIG. 2 is a table showing an elastic curve of a sample surface of Example 1.

FIG. 3 is a configuration diagram of a surface measuring device according to a second embodiment.

FIG. 4 is a table showing an elastic curve of a sample surface of Example 2.

FIG. 5 is a configuration diagram of a surface measuring device according to a third embodiment.

FIG. 6 is a configuration diagram of a surface measuring device according to a fourth embodiment.

FIG. 7 is a configuration diagram of a conventional atomic force microscope.

[Explanation of symbols]

 1 sample 2 spring member 3 probe 4 displacement sensor 5 vibrating element 6 oscillator 12 effective value circuit 14 computer 15 indicator

Claims (4)

[Claims] 1. A probe having a fixed end and supported by a spring member, and a displacement sensor for detecting the displacement of the probe, the probe searches the surface of a sample, and the displacement is measured by the displacement. In a surface measuring instrument that detects the surface state of the sample by detecting with a sensor, a vibrating element that excites the spring member, an oscillator that vibrates the vibrating element at a plurality of frequencies, and an output of the displacement sensor are processed. A surface measuring instrument comprising: a signal processing circuit for detecting the vibration amplitude or phase thereof; and a recorder for recording and displaying the output of the signal processing circuit. 2. The surface measuring device according to claim 1, wherein the oscillator displaces the spring member in a pulse shape. 3. The surface measuring instrument according to claim 1, further comprising a control circuit for feeding back an output of the signal processing circuit to the oscillator. 4. A fine movement mechanism for finely moving the sample in a direction perpendicular to the surface of the sample, and a control circuit for feeding back the output of the signal circuit to the fine movement mechanism. Surface measuring instrument.