JPH03148007A - Surface measuring apparatus - Google Patents

Abstract

PURPOSE:To remove the distortion of an image resulting from the change of the amplitude of a needle by providing a means for vibrating the needle and a means for maintaining the frequency/amplitude of the needle constant at all times. CONSTITUTION:A needle 1 is vibrated when an alternating voltage V (frequency (f)) of an oscillator 3 is impressed to a piezoelectric body 2. As the needle 1 is in touch with a sample 4 more strongly, an electromotive force of the frequency (f) of a piezoelectric plate 5 is increased. A feedback circuit 6 detects the electromotive force of the piezoelectric plate 5, takes out and rectifies a voltage of the components of the frequency (f), and maintains the distance between the needle 1 and sample 4 constant by a minute driving mechanism 7 so that the voltage is kept constant. Moreover, the needle 1 is moved along the surface of the sample 4 by the action of the circuit 6 and a scanning circuit 8, and the locus of the needle is indicated at a display part 9. Further, the mechanism 7 is provided with a piezoelectric plate 10 to detect the vibration of the piezoelectric body 2. A feedback circuit 11 detects an electromotive force S of the piezoelectric plate 10, rectifies a voltage of the components of the frequency (f), and controls an output voltage V of the oscillator 3 so that the voltage is maintained constant. Accordingly, even when the resonance frequency of the vibrating body is changed as a result of the deformation of the mechanism 7, the amplitude of the needle 1 is kept constant.

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD 1 The present invention relates to an apparatus similar to a scanning tunneling microscope (STM), and particularly to a surface measuring apparatus suitable for measuring the surface of an insulator. 2. Description of the Related Art In conventional STM, in which a needle is scanned over a sample surface while keeping a constant current flowing between the needle and the sample, it is difficult to observe the surface of an insulator. Therefore. No. 63-309803 describes a method of vibrating a needle using a crystal oscillator and detecting changes in resonance frequency due to contact between the needle and a sample.

[Problem to be solved by the invention]

When the vibrating needle is scanned, the amplitude changes. Changes in the amplitude of the needle cause distortion in the height direction in the bird track image and uneven intensity in the plane image. An object of the present invention is to eliminate image distortion caused by changes in the amplitude of the needle.

[Means to solve the problem]

The needle is scanned by a modification of the scanning mechanism. Therefore, the mechanical resonant frequency of the system consisting of the needle and scanning mechanism changes as the needle scans. If the frequency of the button is set close to the mechanical resonance frequency of this system, the amplitude of the needle will also change as the needle scans. To solve this problem, the resonant frequency of the scanning mechanism and the frequency of the needle can be shifted. To this end, for example, the rigidity of the scanning mechanism is increased so that the scanning mechanism does not resonate due to the vibration of the needle. Alternatively, a means is provided to detect the vibration of the needle and keep the amplitude constant.

[Effect]

If the lowest resonant frequency of the scanning mechanism is higher than the frequency of the needle, operation of the scanning mechanism will not cause a change in the vibrational state of the needle. When the amplitude changes due to the scanning of the needle, the amplitude can be kept constant by the action of a feedback system that detects the amplitude and keeps it constant.

【Example】

An embodiment of the present invention will be described below with reference to FIG. [needle] indicates that the AC voltage ■ (frequency f) of the oscillator 3 is the piezoelectric body 2
It vibrates by being applied to it. A piezoelectric plate 5 is attached to the sample 4. The stronger the contact between the needle 1 and the sample 4, the greater the electromotive force at the frequency f of the piezoelectric plate 5. The feedback circuit 6 detects the electromotive force of the piezoelectric plate 5, extracts the voltage of the frequency f component, rectifies it, and uses the fine movement mechanism 7 to adjust the distance between the needle 1 and the sample 4 so that this value is kept constant. Keep it constant. The scanning circuit 8 moves the needle 1 to the sample 4 using the fine movement mechanism 7.
Scan along the surface in a rask manner. By the action of the feedback circuit 6 and the scanning circuit 8, the needle 1 moves by tracing the irregularities on the surface of the sample 4. By displaying the trajectory of the needle 1 on the display section 9, the shape of the surface of the sample 4 can be obtained. On the other hand, a piezoelectric plate 10 is attached to the fine movement mechanism 7,
Vibrations of the piezoelectric body 2 are detected. Feedback circuit 1] is piezoelectric plate 1
The oscillator 3 detects the electromotive force S of 0, extracts the voltage of the frequency f component, rectifies it, and keeps this value constant.
The output voltage V is controlled. This allows needle 1. Piezoelectric body 2
．． Even if the resonance frequency of the vibrating body constituted by the fine movement mechanism 7 changes due to the operation (deformation) of the fine movement mechanism, the amplitude of the needle 1 is kept constant. Note that the contact between the needle 1 and the sample 4 has almost no effect on the electromotive force of the piezoelectric plate 10. FIG. 2 shows the fine movement mechanism 7. Piezoelectric body 2. A specific example of the configuration of the needle 1 will be shown. The fine movement mechanism 7 is composed of three piezoelectric elements 12, 13, and 14 that are perpendicular to each other, and the intersection point of the piezoelectric elements 12, 13, and 14 makes fine movements in three dimensions. Although not shown, the other ends of the three piezoelectric elements are fixed. The piezoelectric body 2 and the needle 1 are attached to this intersection. The piezoelectric elements 13 and 14 are for scanning the needle 1, and a voltage is applied from the scanning circuit 8. The piezoelectric element 12 is used to control the distance between the needle and the sample and to detect vibrations of the piezoelectric body 2 at the same time. Therefore, one electrode is connected to the feedback circuit 6 and the other electrode is connected to the feedback circuit 11. The resistor 15 is for removing the low frequency component voltage applied from the feedback circuit 6. A signal S whose low frequency components have been cut by the capacitance of the piezoelectric element 12 and the resistor 15 is input to the feedback circuit 11 . FIG. 3 shows another configuration example. The basic configuration is almost the same as the previous embodiment, but the piezoelectric element 12 is provided with a feedback circuit 6.
The piezoelectric element 21 for amplitude detection is attached to the base of the needle 1-. The electromotive force S of this piezoelectric element 2 is input to the feedback circuit 11. In this way, the piezoelectric element for amplitude detection is placed at the tip of the scanning mechanism.
By attaching it near the needle 1, the amplitude of the needle 1 can be measured accurately. If the piezoelectric element for amplitude detection is mounted at a position away from the needle 1, the mounting will measure a position-specific amplitude, which does not necessarily match the amplitude of the needle 1. FIG. 4 shows an embodiment in which the problem was solved by lowering the resonance point of the fine movement mechanism. Needle 1. Piezoelectric body 2, sample 4.
The piezoelectric plate 5 is similar to the above embodiment, but a fine movement mechanism 16 is attached to the piezoelectric body 2, and the needle 1 is attached to the tip of the fine movement mechanism 16. The maximum dimension (length in the polarization direction) of the fine movement mechanism 16 is considerably shorter than the length of the short side of the piezoelectric plate 5. FIG. 5 shows a detailed configuration of the fine movement mechanism 16 shown in FIG. 4. Electrodes are attached to the six metal surfaces of a rectangular parallelepiped piezoelectric body.
An electric field is applied in the polarization direction and in two directions perpendicular to the polarization direction. The signal from the feedback circuit 6 is applied to the electrode 17, and the signal from the scanning circuit 8 is applied to the electrodes 18 and 19. All electrodes facing these electrodes are at ground potential. The distance between the needle 1- and the sample 4 is controlled by the electric field applied in the polarization direction, and the electric field in the direction perpendicular to the polarization direction shear deforms the piezoelectric material and causes the needle to scan in a direction parallel to the sample surface. The piezoelectric body 2
By vibrating the needle 1., the force interaction between the needle 1. and the sample 4 can be detected efficiently. Fine movement mechanism 16. Since the resonant frequency of the system made up of the piezoelectric body 2 is higher than the F resonant frequency of the piezoelectric plate 5, there is no change in the vibration state even if the fine movement mechanism 16 is deformed, and therefore, the amplitude of the needle 1 is also unchanged. In the embodiments described above, the structure for supporting the scanning mechanism and the sample has been omitted. In reality, as shown in FIG. 6, there is a support section 20 including a coarse movement mechanism for bringing the needle 1 close to the sample within the displacement range of the fine movement mechanism. For this reason, the resonance point of the system including the support portion 20 must also be considered. The lower the frequency of the piezoelectric body 2, that is, the longer the long side of the piezoelectric plate 5, the easier it is to avoid resonance in mechanical systems other than the piezoelectric plate 5. Since the entire mechanism including the support section 20 is isolated from other parts, there is no need to consider any further system. If anything other than the piezoelectric plate 5 resonates, the distance between the needle 1 and the sample 5 will oscillate. Furthermore, the vibration of the piezoelectric body 2 entering the piezoelectric plate 5 through the support portion 20 becomes extremely large. At this time, if this resonance state changes due to the operation of the fine movement mechanism 7, the vibration that enters through the support portion 20 changes according to the scanning of the needle. As a result, even if the amplitude of the vibration detected by the piezoelectric plate 5 is kept constant, the amplitude of the vibration detected when the needle 1 pokes the sample 4 cannot be kept constant. That is, the feedback circuit 6 cannot maintain a constant force interaction between the needle 1 and the sample 4. In this embodiment, this problem can also be solved. [Effects of the Invention] According to the present invention, in a method of measuring the surface shape of a sample by vibrating a needle and scanning the vibrating needle along the sample surface, the vibration state caused by scanning the needle, etc. Image distortion caused by changes in can be removed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIGS. 2 and 3 are perspective views showing the configuration of the scanning mechanism section in FIG. 1, and FIG. 4 is a block diagram showing the configuration of an embodiment of the present invention. Perspective view shown, fifth
This figure is a perspective view showing the structure of the scanning mechanism section in FIG. 4, and FIG. 6 is a schematic side view showing the structure of the entire surface measuring device mechanism section. Explanation of symbols

Claims (1)

[Claims] 1. A surface measuring device having a needle with a sharply pointed tip and a scanning means for scanning the needle along the sample surface,
A surface measuring device comprising means for vibrating the needle and means for always keeping the vibration amplitude of the needle constant. 2. The surface measuring device according to claim 1, wherein the resonant frequency of the scanning means is higher than the vibration frequency of the needle. 3. In the surface measuring device according to claim 1, the scanning means is a hexahedral piezoelectric body, and has means for applying an electric field in a direction perpendicular to each surface of the piezoelectric body. A surface measuring device characterized in that the polarization direction of is perpendicular to a specific surface of the piezoelectric body. 4. A surface measuring device according to claim 1, further comprising vibration detecting means and means for controlling the vibration amplitude of the needle based on a signal from the vibration detecting means.