CN1632518A - Measurement Method of Atomic Force Microscope Based on Angle Measurement - Google Patents

Abstract

This invention discloses an atomic force microscope measurement method based on angle measurement, which belongs to the test technique of the signals of atomic force microscope APM probe and cantilever. This method adopts angle sensor by which the rotation angle of the probe is measured and is converted into the electrical signals at a proportion with the angle change value. It gets the angle change of the cantilever caused by the measurement force through signal analysis and process and further to get the surface outline of the object pf the probe.

Description

Measurement Method of Atomic Force Microscope Based on Angle Measurement

Technical field

The invention relates to an atomic force microscope measurement method based on angle measurement, which belongs to a detection method of a probe/cantilever beam signal of an atomic force microscope (AFM).

Background technique

When the end of the cantilever beam is stressed, two deformations will occur at the end, one is deflection and the other is rotation angle. The atomic force microscope uses the probe at the tip of the micro-cantilever beam. When the probe approaches or touches the surface of the object to be measured, there will be a force interaction between the probe and the sample, and the force will cause the micro-cantilever beam to bend. Therefore, The change of the bending amount of the micro-cantilever can be detected in two ways, that is, measuring the change of the deflection of the micro-cantilever of the atomic force microscope, or measuring the change of the tip rotation angle of the micro-cantilever of the atomic force microscope.

At present, the type of instruments represented by atomic force microscopes that obtain the surface information of the measured object by detecting the bending change of the micro-cantilever beam all use the measurement of the deflection change of the micro-cantilever beam after being stressed, such as the multifunctional atomic force microscope of the American Veeco company. , Japan's Seiko's atomic force microscope, etc., when the laser hits the micro-cantilever beam, due to the change in the deflection of the micro-cantilever beam, the deflection of the reflected light is caused, and the position of the light spot on the photodetector changes. By detecting the position of the light spot The amount of change, so as to obtain the amount of deflection change of the micro-cantilever beam, and then obtain the amount of change in force measurement and the surface profile of the object. Although this method is simple in structure and suitable for commercial production, in the scanning process of this type of microscope under the constant force mode, due to the change of the position of the fixed end of the probe, the error of the measurement principle is introduced. To obtain high-precision measurement results, it is necessary to Make error corrections or strict corrections.

Contents of Invention

The object of the present invention is to provide a measurement method of atomic force microscope based on angle measurement, which can overcome the principle error and subsequent correction problems introduced by the existing method of measuring the probe deflection of atomic force microscope, and can reduce the impact of the existing method on the Measure the limitations of the sample shape, volume, weight, etc., and expand the scope of application of the atomic force microscope.

The object of the present invention is achieved like this: based on the AFM measurement method of angle measurement, the method adopts an angle measurement type atomic force microscope measurement device, and the cantilever beam displacement measurement device of the atomic force microscope adopts an optical differential angle sensor, and the angle measurement The sensor includes a collimated light source, a converging lens, a 1/4 wave plate, a polarizing beam splitter, a beam splitter, two critical angle prisms, and two photodiodes. The method is characterized in that after the incident light is converged, it is vertically incident on the probe surface of the atomic force microscope, and the deflection angle of the reflected light is detected by the angle measurement sensor, and the reflected laser carries the angle change information of the cantilever beam into the angle measurement device; The measurement device adopts the optical differential measurement method. In this method, the output signal of the angle measurement device is zero when the initial force measurement is set. When the force measurement changes during the scanning process, the bending angle of the cantilever beam changes. It is detected by the angle measuring device and converted into an electrical signal proportional to the angle change value; the electrical signal is amplified and then analyzed and processed to obtain the angle change of the cantilever beam caused by the change of the force measurement, and then obtain the measured value of the probe. Force variation/object surface topography profile.

The advantage of the present invention is that the in-plane scanning (XY) driving device is separated from the longitudinal (Z) tracking driving device, the sample stage is combined with the XY scanning driving device, and the sample stage only performs in-plane scanning; the probe passes through the probe holder Combined with the Z-direction tracking driver, the separation of Z-direction and XY-direction motion is realized, thereby reducing the limitation of the shape, volume, weight, etc. of the sample to be measured, and expanding the scope of application of the atomic force microscope. In the constant force mode, the position change of the fixed end of the probe will not affect the measurement of the rotation angle. Therefore, this method can overcome the principle error introduced by the deflection measurement method and its subsequent correction problems.

Description of drawings

Fig. 1 is a schematic diagram of the device structure for realizing the method of the present invention.

Figure 2 is a schematic diagram of the AFM measurement method based on angle measurement

In the figure: 1 and 8 are critical angle prisms, 2 is a beam splitter integrated with a 1/4 wave plate, 3 is a polarizing beam splitter integrated with a 1/4 wave plate 5, 4 is a semiconductor laser integrated with a converging lens, 6 PZT is the piezoelectric ceramic driver for Z-direction tracking, which integrates the AFM probe holder and AFM probe, and 7 and 9 are photoelectric receivers.

Detailed ways

The AFM measurement method based on angle measurement uses an optical differential angle measurement device to detect the change in the rotation angle of the micro-cantilever beam of the atomic force microscope. The process is as follows: the light emitted by the semiconductor laser 4 first converges through the lens, and after passing through the polarizing beam splitter 3, The original beam is divided into S-polarized light and P-polarized light. After the S-polarized light is reflected, it passes through the 1/4 wave plate 5 and becomes circularly polarized light. It is incident on the reflective surface of the probe 6 of the atomic force microscope and is reflected back from the surface of the AFM probe. Circularly polarized light, the circularly polarized light carries the change information of the cantilever beam’s rotation angle, becomes P polarized light after passing through the 1/4 wave plate, and then splits into two mutually orthogonal beams of equal energy after passing through the beam splitter 2, and its polarization state remains unchanged. Respectively incident into two prisms 1 and 8 arranged along the right angle direction, the intensity of the outgoing light is detected by photoelectric receivers 9 and 7 respectively; at the initial force measurement setting value, it can be considered that the output signal of the angle measuring device is "zero" ; When the measuring force changes during the scanning process, the bending angle of the cantilever beam changes, and the reflected light, that is, the incident light relative to the angle measuring device, also has a corresponding change in its incident angle, which is the micro-cantilever angle change amount Twice the measured value is magnified.

Due to the differential measurement method, the reflected light from the cantilever beam is divided into two beams by the half-mirror 2, and then enters into two prisms respectively, that is, the two parts (1) and (2) in Fig. 1. When the reflection When the angle of light is deflected, the incident angles of the incident light of the two prisms increase/decrease Δθ respectively, and the reflectivity changes also increase or decrease respectively. The light intensity of the outgoing light is detected by the photodiode and converted into light Current, the two-way photocurrent signal undergoes current-voltage conversion and addition, subtraction and division operations to obtain the angle change after linearization, that is, the change is detected by the angle measuring device and converted into a value proportional to the angle change. electric signal. The electrical signal is amplified and then analyzed and processed to obtain the angle change of the cantilever beam caused by the change of force measurement. Since there is a certain proportional relationship between the angle of the tip of the AFM probe/cantilever beam and the deflection, the surface of the object can be obtained according to this relationship. High and low changes, and then obtain the force measurement changes of the probe/surface topography of the object.

Claims (1)

1. An atomic force microscope measurement method based on angle measurement, realizing the method adopts an angle measurement type atomic force microscope measurement device, and the cantilever beam displacement measurement device of the atomic force microscope adopts an optical differential angle sensor, and the described angle measurement sensor includes a collimator Light source, converging lens, 1/4 wave plate, polarized beam splitter, beam splitter, two critical angle prisms, two photodiodes; the method is characterized in that after the incident light is converged, it is vertically incident on the probe surface of the atomic force microscope. The deflection angle of the reflected light is detected by the angle measurement sensor, and the reflected laser carries the information of the change in the rotation angle of the cantilever beam into the angle measurement device; the angle measurement device adopts an optical differential measurement method. The output signal of the angle measuring device is zero. When the measuring force changes during the scanning process, the bending angle of the cantilever beam changes, and the change is detected by the angle measuring device and converted into an electrical signal proportional to the angle change value; the electrical signal After amplification, the signal is analyzed and processed to obtain the angle change of the cantilever beam caused by the change of force measurement, and then the change of force measurement of the probe/surface topography of the object is obtained.

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