JP2580750Y2 - Atomic force microscope - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical lever type atomic force microscope for converting an atomic force acting between materials into a displacement by a minute spring element.

[0002]

2. Description of the Related Art Atomic force microscope
ce Microscope) is the author of G.S. Invented by Binnig et al. (Physical
Review Letters vol. 56 p93
0 1986), it has been expected as a new means for observing the surface shape of an insulating material, and research has been advanced. The principle is that the atomic force acting between the detection chip and the sample, whose tip is sufficiently sharpened, is measured as the displacement of the spring element to which the detection chip is attached, and the sample is maintained while keeping the displacement of the spring element constant. Scanning the surface, a control signal for keeping the displacement amount of the spring element constant as shape information,
The shape of the sample surface is measured.

The means for detecting the displacement of the spring element is roughly classified into an STM method using a tunnel current and an optical method. S
The TM system utilizes a so-called tunnel phenomenon in which a current starts to flow when two conductors are brought close to a distance of several nm to several Å and a voltage is applied. Conductivity is given to the spring element, and a sharp metal needle is brought close to the spring element to about 1 nm to flow a tunnel current, and the current value is controlled as a displacement signal of the spring element.

As an optical system, an example using a so-called interference method itself (Journal of Vacuum Sci)
ence Technology A6 (2) p266
Mar / Apr 1988) and examples of the optical lever method (Jo
urnal of Applied Physics
65 (1), 1 p164 January 198
9) has been reported. In the case of the optical lever system, a gas laser such as helium neon was used in consideration of stability when the atomic force microscope was invented as a light source, but an apparatus using a semiconductor laser is now commercialized.

FIG. 3 shows the principle of operation of the atomic force microscope.
FIG. 3A is a conceptual diagram showing a relationship between an interatomic distance and an interatomic force. When two atoms are brought closer to a distance of several nm or several Å, a so-called van der Waals force that is proportional to the minus 7th power of the interatomic distance is generated as a force that attracts each other. When it is brought closer, the so-called exchange repulsion rises sharply. FIG. 3B is a sectional view showing how the spring element 3 is displaced. The atomic force microscope scans the sample 1 in the Z direction so that the displacement x in the figure is constant, and scans the sample in the in-plane direction to obtain shape data of the sample surface.

[0006]

However, in a conventional optical lever type atomic force microscope using a laser, the coherent light of the laser, which is a coherent light, causes the coherence of the laser to measure the periodic sample from the sample. Reflected light interferes on the photodetector, causing an error in the measured data.

FIG. 2 is a schematic view showing a state in the vicinity of a conventional optical lever type spring element. Laser light 11 is irradiated on the back surface of the spring element 3, and a part of the light is reflected as reflected light 12. Part of light 11 transmitted through spring element 3 and spring element 3
The light 11 deviated from the surface is scattered on the sample surface, and a part thereof becomes the reflected light 13. The spring element 3 is required to be a weak spring of 1 Newton per meter or less, is made with a thickness of several hundred nm by semiconductor technology, and the base material is transparent. Therefore, a reflective film is necessary, but if the film thickness is increased to increase the reflectance, the spring stiffness also increases, so that a sufficient reflective film cannot be provided. As a result, it is difficult to completely remove the reflected light 13. is there. When a diffraction grating is measured as the sample 1 in this state, the reflected light 13 from the upper stage of the diffraction grating is measured.
a and the reflected light 13 b from the lower stage of the diffraction grating interfere with each other to generate interference fringes on the photodetector 9. Fine movement element 4 for measurement
Is scanned in the X direction, the interference fringes on the photodetector 9 also move in conjunction with the scanning, resulting in an error in the measurement data. A similar problem occurs when measuring a sample having a periodic structure of several μ to several tens of μ such as an IC pattern.

[0008]

In order to solve the above-mentioned problems, in the present invention, an optical lever type displacement detecting system is constituted by using an LED having no coherence as a light source.

[0009]

With the above arrangement, the LED is close to natural light and exhibits little coherence.
Even with a sample having periodicity such as a pattern, an interference phenomenon does not occur on the photodetector, and accurate measurement data can be obtained.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of the atomic force microscope according to the present invention. A detection chip 2 for limiting the interaction with the sample 1 to a minute range is attached to the spring element 3 to constitute a minute force detector. The tip of the detection chip 2 is sharp. The sample 1 is fixed to the fine movement element 4, and the tip of the detection chip 2 is driven three-dimensionally in the region of the surface of the sample 1 where an atomic force acts. The sample 1 is scanned with high resolution in the direction of the sample plane by the fine movement element 4 while adjusting the distance in the direction perpendicular to the sample plane with respect to the spring element 3. Fine movement element 4 is sample 1
And the rough positioning of the spring element 3 and the tip of the detection chip 2 are fixed to the coarse movement mechanism 5 for bringing the tip of the sample 1 closer to the region where the atomic force acts on the surface of the sample 1.

On the back side of the spring element 3, a displacement detection system for detecting the amount of displacement of the spring element 3 is provided. First, light emitted from the LED 6 is applied to the spring element 3 by the lens 8.
Is focused on the front end of the back surface of the. The reflected light is condensed on the split-type photodetector 9 via the mirror 7. In the case where, for example, a two-segment type photodetector is used as the light detection element 9, the difference between the two-segment elements is obtained by adjusting the light so that the light is uniformly incident on the divided elements in advance. When the spring element 3 is pushed by the sample 1 and tilts,
The light spot on the light receiving surface of the photodetector also moves in proportion to the inclination of the spring element 3, and the output of the splitting element increases on one side and decreases on the other side. As a result, the difference output is proportional to the inclination of the spring element 3, that is, the displacement. This displacement signal is taken into the servo system and converted into a control signal to the fine movement element 4 and the coarse movement mechanism 5, and is controlled so that the distance between the sample 1 and the spring element 3 becomes constant.

[0012]

According to the present invention, as described above, by using an LED as the light source of the optical lever displacement detection system, even if the sample has periodicity such as a diffraction grating or an IC pattern, the interference phenomenon can occur on the photodetector. It does not occur and accurate measurement data can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of an atomic force microscope according to the present invention.

FIG. 2 is a schematic view showing a state in the vicinity of a conventional optical lever type spring element.

FIG. 3 is a diagram showing a relationship between an interatomic force and an interatomic distance;
(A), (b) is a partial sectional view showing a spring element and displacement.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sample 2 Detection chip 3 Spring element 4 Fine movement element 5 Coarse movement mechanism 6 Light source (LED) 7 Mirror 8 Lens 9 Light detection element

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01B 21/30 G01N 37/00 G01B 7/34 G01B 11/00-11/30

Claims (2)

(57) [Scope of request for utility model registration] 1. A displaced by an atomic force received detection chip Togarashi tip from the sample surface, said detection chip to the end portion
A spring element having a loop, and a light-generating back end of the spring element.
A light source that irradiates a surface , a photodetector that detects a displacement of light reflected on the back surface of the end of the spring element, and a three-dimensional relative movement of the sample and the spring element, and a tip of the detection chip is A coarse movement mechanism for approaching the region where the atomic force acts on the sample surface, and a fine movement mechanism for moving the tip of the detection chip attached to the spring element three-dimensionally in the region where the atomic force acts on the sample surface. An atomic microscope comprising: a control unit that keeps a constant distance between the sample and the tip of the detection chip via the fine movement mechanism, wherein the light source is a light source having no coherence. Atomic force microscope. 2. An atomic force microscope, wherein the light source is LE.
2. The atomic force microscope according to claim 1, wherein D is D.