JPH07159418A - Scan type probe microscope - Google Patents

Abstract

PURPOSE:To provide a scan type probe microscope of which cantilever can be exchanged with high reproducibility and of which optical adjustment of a displacement detection system is easy. CONSTITUTION:The body 40 of a sensor has a laser diode 12, a collimation lens 16 and an objective lens 18 mounted thereon and a cantilever 20 is arranged therebelow. The cantilever 20 is mounted on a cantilever support base 26. The cantilever support body 26 is fixed on the body 40 of the sensor through a parallel spring movable biaxially. The sensor body 40 is provided with an x screw and a y screw to move the cantilever 20 in directions X and Y. A condenser lens 34 and a 2-split photo detector 32 are mounted on a biaxial stage 38 of the photo detector fixed on the sensor body 40. A sample 28 is placed on a piezo-electric body 62 mounted on a coarse action approach mechanism 64.

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 which detects a force acting between a probe and a sample and observes the sample based on the detected force.

[0002]

2. Description of the Related Art Atomic force microscopes and magnetic force microscopes are well known as scanning probe microscopes for observing a sample based on the force acting between the probe and the sample. In this type of scanning probe microscope, the detection of the force acting between the probe and the sample usually occurs because the probe is provided at the free end of the flexible cantilever that elastically deforms and the probe receives the force. This is done by examining the displacement of the free end of the cantilever.

As a cantilever displacement detection system for detecting this displacement, there are a cantilever displacement detection system, an interferometry method, a focusing detection method, and an angle detection method. The interferometry method irradiates a laser beam on a mirror provided on the surface of the free end of the cantilever on the opposite side of the probe, and changes the optical path length caused by the displacement of the cantilever using an interferometer. Is detected and the displacement of the cantilever is obtained based on the change in the optical path length. The focus detection method detects the focus state of the beam projected from the cantilever mirror to the optical receiver through an optical element such as a critical angle prism, a cylindrical lens, or a knife edge, and based on the focus state. This is a method of obtaining the displacement of the cantilever. The angle detection method is a method in which an angle change of the beam reflected by the cantilever is detected by a two-divided light receiving element, and the displacement of the cantilever is obtained based on this angle change.

Among these various detection methods, the optical lever method, which is one of the angle detection methods, is generally used because of its simple structure and high detection sensitivity. FIG. 5 shows an example of a cantilever displacement detection system using the optical lever method. The laser beam 14 from the laser diode 12 passes through the collimator lens 16 to become parallel light, and the objective lens 18
The light is focused on the mirror 24 and is focused on the mirror 24 provided at the free end of the cantilever 20 on the opposite side of the probe 22. The cantilever 20 has a cantilever holding base 26.
For example, it is attached at an angle of about 10 degrees. After being reflected by the mirror 24, the laser beam 14 is reflected again by the fixed mirror 30 and enters the two-divided light receiving element 32.

The cantilever 20 has a length of 100 to 200.
μm, width 50 μm, thickness 0.4 to 4 μm Si ₃
It is a minute component of N ₄ thin film, and the length of the probe 22 at its free end is as short as 6 μm. The laser beam 14 is adjusted by using the moving device of the laser diode 12, the Z moving device, etc. so that the incident beam surely irradiates the mirror 24 and the reflected beam straddles the bisector of the bisected light receiving element 32. It

When the cantilever 20 is a rectangular thin plate, its length is L, its thickness is a, its width is b, and its elastic coefficient is E.
Then, the relationship between the force f and the displacement ΔZ is given by the following equation. ΔZ = 4L ³ f / a ³ bE (1) The acting force f is the atomic structure of the tip of the probe 22 and the sample 28.
The combination of atomic structure of the surface of, and physical and chemical force determined by the approach distance (frictional force, the suction force, adhesion force, electrostatic force, Coulomb force, van der Waals forces, etc.), its size is 10 ^{- 5} N / m to 10 ^-12 N / m
In a wide range, the cantilever 20 and its displacement detection system are required to have various measures. Thus, the size of the cantilever 20 is selected to accommodate a wide range of forces.

FIG. 6 shows the relationship between the distance Z between the probe 22 and the displacement of the free end of the cantilever (the force f acting between the two) when the probe 22 of FIG. Is a f-Z curve (force curve, movement cycle diagram) in which the vertical axis represents the displacement (force f) and the horizontal axis represents the distance Z.

In FIG. 6, a point where no force is applied between them (that is, f = 0), for example, a point where Z = 1 μm is set as a point O, and the probe 12 is brought closer to the sample 28 from this point O. Then, the force f is received from a point after passing the point A, and the cantilever 20 starts to be displaced. The force f initially received is an attractive force, and f is indicated by a negative sign.

When the probe 22 is further brought closer to the sample 28, the attractive force is increased in the negative direction, but the point C passes through the polarization point B and then the point C.
Reaches the peak at. This area of A → B → C is referred to as a first attractive area FS1. From around the point B, the probe 22 begins to be affected by the repulsive force, and the increasing gradient of the attractive force weakens and the increasing gradient of the repulsive force increases. After passing the point C, the repulsive force becomes dominant this time, and after the point C, the fZ curve becomes a steep straight line. The second attractive area F up to the point D where the attractive force and the repulsive force cancel each other out.
It is called S2, and the point D and the points thereafter are called repulsive force region FR.

Next, when the probe 22 is moved away from the sample 28 from an appropriate point E in the repulsive force region FR, the straight line when approaching is first moved backward, but after entering the second attractive force region FS2. Does not go to the point C, but is a curve D → F → G due to the control of the attractive force due to the surface tension along the side surface of the probe 22 and the attraction force due to polarization.
After that, the cantilever 20 is released from the acting force and returns to the line of f = 0 at the point H.

A, B, C of the characteristic points of these fZ curves,
The values of D, E, F, G, and H (f, Z) take various numerical values depending on the combination of the probe 22 and the sample 28 and the physical / chemical conditions. In the measurement by the atomic force microscope, a force curve is taken at one point on the sample 28 under a predetermined physical / chemical condition, and the force curve is analyzed. Further, a predetermined region on the force curve (first attractive region FS1, By setting a reference point in the second attractive region FS2, repulsive force region FR) and scanning the probe 22 along the surface of the sample 28 while performing feedback control so as to maintain this reference point in the region, Multi-dimensional images can be obtained by obtaining physical and chemical properties of the surface.

[0012]

In the optical lever method, for example, in FIG. 5, the laser beam 14 from the laser diode 12 is made incident on the mirror 24 of the cantilever 20, and the reflected beam is on the bisector of the bisected light receiving element 32. It is necessary to make the laser diode 12 move in the XY directions and to divide the light into the two-divided photodetector 32.
Is dealt with by moving in the Z direction. The adjustment by such a method has some problems as described below.

Since the three elements, the cantilever, the laser diode and the light receiving element, have strong correlation interference, it is not easy to adjust each of them independently and randomly. Also,
If the position of the laser beam moves, the scanning center and the position of the probe will shift each time the cantilever is replaced.

The movement adjustment mechanism must be stiff to achieve the measurement. Conventionally, this movement adjusting mechanism is a stage having two sliders, is fixed by a magnet, or is screwed by three-point support. It is difficult to increase the rigidity of a stage having two sliders, and the stage itself becomes large. In the case of fixing with a magnet, the structure of the cantilever becomes large, such that the direction of the cantilever rotates or a surface that defines the adjustment direction is provided. If there is no surface that defines the adjustment direction,
When the cantilever is replaced, the position where the cantilever was before is displaced and it becomes difficult to find the position. Similarly, in the case of screwing with three-point support, the direction of the cantilever also rotates, and it is very difficult to grasp and adjust the moving direction.

Further, the larger the NA of the optical system for irradiating the cantilever with the laser beam, the smaller the spot of the laser beam on the cantilever, and it becomes easier to avoid the situation where the spot protrudes from the back surface of the cantilever. On the other hand, the divergence angle of the reflected laser beam from the cantilever also becomes large, and a light receiving element having a large light receiving surface must be used.

Further, in the correction amount of the reflection position due to the warp due to the processing error of the cantilever, in the structure in which the reflected beam is directly incident on the light receiving element, the necessary adjustment movement amount of the light receiving element becomes large, and the entire structure becomes large. If the amount of adjustment movement is large, it is difficult to increase the rigidity of the movement adjustment mechanism.
It is an object of the present invention to provide a scanning probe microscope in which cantilevers can be replaced with good reproducibility and the optical adjustment of the displacement detection system can be easily performed.

[0017]

SUMMARY OF THE INVENTION The present invention is a scanning probe microscope for observing a sample using a probe supported at the free end of a cantilever, and the free end of the cantilever opposite to the side having the probe. A reflection surface provided on the light source, a light source for emitting a laser beam, a beam irradiation means for making the laser beam incident on the reflection surface of the cantilever at a predetermined angle, and a light receiving element for receiving the reflected laser beam reflected by the reflection surface. , Equipped with an optical lever sensor having a detection means for detecting the angle change of the reflected laser beam and detecting the displacement of the probe based on this, the light source is fixed, the light receiving element and the cantilever move for optical adjustment Supported as possible.

[0018]

Since the light source for emitting the laser beam, for example, the laser diode is fixed, high rigidity is secured. The cantilever is frequently replaced due to its low durability, and it is necessary to adjust the relative positions of the cantilever, the laser diode, and the light receiving element each time it is replaced. For this reason, in the conventional method in which the laser diode and the light receiving element are moved to perform optical adjustment, both the laser diode and the light receiving element must be moved and adjusted for each replacement according to the position and processing accuracy of the cantilever. In the present invention, the laser diode is fixed, and the optical adjustment of the optical lever sensor is performed by adjusting the positions of the cantilever and the light receiving element. It only needs to be moved by the difference in the error, and the light-receiving element need only be moved by the difference in the machining error of the cantilever sled before and after the replacement.

Further, the position where the spot of the laser beam falls becomes constant, the position of the probe of the cantilever can be always kept constant, and the center of scanning and the position of the probe can be made constant.

More preferably, the cantilever is supported by a parallel spring having a bearing surface for biaxially movable cantilever mounting. In this way, if there is an abutment surface at the cantilever mounting position on the parallel spring, the mounting position of the cantilever before the replacement and the mounting position of the cantilever after the replacement become substantially coincident with each other. Therefore, the position adjustment of the cantilever and the laser beam is small, and the required moving amount of the cantilever is about the moving amount of the parallel spring. Although the parallel spring has a small stroke, it has high rigidity and can be made compact. Further, this cantilever positioning mechanism is so small that the axis shift due to rotation or the like can be ignored. In particular, it is important to make the periphery of the cantilever compact and highly rigid, and this configuration enables stable atomic force microscope measurements.

It is more preferable to dispose a convex lens between the light receiving element and the cantilever. Since the laser beam reflected by the cantilever is condensed by the convex lens and is incident on the light receiving element, the reflection angle of the reflected light from the cantilever becomes small, so even if there is a processing error in the cantilever warpage, the adjustment amount is small. .

The light receiving area of the light receiving element can be small, and the light receiving element itself can be made small. Although the angle of reflection of the reflected light from the cantilever is reduced by providing the convex lens, the density of the laser on the light receiving element is correspondingly increased, so that the sensitivity of the sensor to the movement amount of the spot is increased. With such a configuration, the entire layout can be downsized, and as a result, a stable scanning probe microscope with high rigidity can be obtained.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show a first embodiment of a sample scanning atomic force microscope according to the present invention.

As shown in FIG. 1, the sensor body 40 and the scanner body 66 are composed of a column 48 fixed to the sensor body 40 and three grooves 6 provided in the scanner body 66.
It is positioned by 8 and.

The laser diode 12, the collimator lens 16, and the objective lens 18 are attached to the sensor body 40 so that their optical axes are vertical. A cantilever 20 is arranged below these optical elements. The cantilever 20 is attached to the cantilever support base 26 in a state of being tilted by 10 degrees with respect to the horizontal plane.

As shown in FIG. 2, the cantilever support 26 is fixed to the sensor body 40 via a parallel spring 42 which is biaxially movable. The sensor body 40 is provided with x-screw 44 and y-screw 46 that move the cantilever support 26, that is, the cantilever 20 in the X direction and the Y direction by advancing and retracting itself in accordance with the rotation operation.

Returning to FIG. 1 again, the laser diode 12
A condenser lens 34 and a two-divided light receiving element 32 are arranged in the direction in which the cantilever 20 reflects the laser beam from. The condensing lens 34 and the two-divided light receiving element 32 are the light receiving element biaxial stage 38 fixed to the sensor body 40.
Is attached to.

A sample 28 is arranged below the cantilever 20. The sample 28 is placed on the piezoelectric body 62 for performing fine movement scanning. The piezoelectric body 62 is attached to a coarse movement approach mechanism 64 for performing coarse movement.

Next, an optical lever sensor for detecting the displacement of the cantilever will be described. The laser beam 14 from the laser diode 12 is collimated by the collimator lens 16, collimated by the objective lens 18, and radiated to the back surface of the cantilever 20 at the focal position. The cantilever 20 is attached to the cantilever holding table 26 by 10
The laser beam 14 is reflected, and after being reflected, enters the condenser lens 34 and is narrowed down.
2 reaches the light receiving surface 36 before the focal position.

The cantilever 20 has a length of 100 to 200.
It is a micro component having a width of 50 μm, a width of 50 μm, and a thickness of 0.4 to 4 μm, and its position is adjusted so that the spot of the laser beam is placed on the back surface of the cantilever every time the cantilever is replaced. Here, in order to position the cantilever, the cantilever 20 has a parallel spring 42 having a biaxial spring element and an x screw 44 and a y screw 4 for translating the biaxial.
6 is attached to the sensor body 40. x screw 4
4 and the y-screw 46 are parallel spring travel points 45,
It is only in contact with 47 and the cantilever is positioned by turning these two screws.

The cantilever is 20 depending on its processing accuracy.
The tip is 0 μm, and the tip is warped up to ± 10 μm from the root. Therefore, the laser beam 14 on the two-divided photodetector 32 caused by the sled and the cantilever mounting error
The displacement from the center of the is adjusted by the light receiving element biaxial stage 38. Since the laser beam reflected from the cantilever 20 is condensed by the condenser lens 34, the amount of movement during adjustment can be small.

Sample 2 under predetermined physical and chemical conditions
A force curve is taken at one point on 8, and a measurement point is set in a region on the force curve, and the surface of the sample 28 is scanned with the measurement point as a reference.

The laser diode 12 is driven by the laser driver 10, and the displacement signal 52 of the cantilever 20 detected by the two-divided light receiving element 32 is amplified by the preamplifier 50 and sent to the host computer 54. In response to an instruction from the host computer 54, the piezoelectric body drive circuit 56 supplies the piezoelectric body 62 with a Z drive signal 60 for keeping the displacement of the cantilever 20 constant. At the same time, the piezoelectric body driving circuit 56 moves the XY for scanning the sample 28 in the XY direction.
The drive signal 58 is supplied to the piezoelectric body 62, and the host computer 54 constructs a three-dimensional uneven image of the sample 28 based on the XY drive signal 58 and the Z drive signal 60, and stores or displays this.

As described above, it is possible to provide an atomic force microscope which has a sensor which is more compact and has higher rigidity than the conventional atomic force microscope and which can be easily adjusted when the cantilever is replaced.

FIG. 3 and FIG. 4 show a second embodiment of the present invention. The present embodiment is an atomic force microscope of the type in which a sensor and a cantilever are scanned. In this embodiment, the sensor body 40 is supported by the piezoelectric body 62 and the coarse movement approach mechanism 64, and the entire sensor body 40 is moved during scanning, which is the only difference from the first embodiment. The other operating principles are exactly the same, so the description is omitted.

The system of the sensor and the cantilever is small in size and has high rigidity. When the system of the cantilever and the sensor is driven by a piezoelectric body, the resonance point lowering and vibration problems caused by the size of the system are ignored. It is possible.

Since the atomic force microscope of this embodiment drives the system of the sensor and the cantilever during scanning,
There are no restrictions on sample size, and large samples can be observed.

[0038]

According to the present invention, it is possible to provide a scanning probe microscope having a cantilever displacement detection system capable of exchanging a cantilever with good reproducibility and easily performing necessary adjustment at the time of exchanging. Therefore, the position of the probe of the cantilever can always be kept constant, and the center of scanning and the position of the probe can be kept constant, so that the measurement data is reproducible and highly reliable.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an atomic force microscope that is a first embodiment of the present invention.

FIG. 2 is a sectional view of the device of FIG. 1 taken along the line II-II.

FIG. 3 is a diagram showing a configuration of an atomic force microscope that is a second embodiment of the present invention.

FIG. 4 is a view of the device of FIG. 3 viewed from the direction of arrow IV.

FIG. 5 shows a conventional example of a cantilever displacement detection system using an optical lever method.

FIG. 6 shows a relationship between a distance Z between the probe and a force f acting between the probe and the probe when the probe approaches and retracts from the sample surface.
It is the figure which showed the Z curve.

[Explanation of symbols]

12 ... Laser diode, 20 ... Cantilever, 32
... two-divided light-receiving element, 38 ... light-receiving element biaxial stage, 44
... x screw, 46 ... y screw.

Claims (3)

[Claims] 1. A scanning probe microscope for observing a sample using a probe supported at the free end of a cantilever, comprising: a reflecting surface provided at the free end of the cantilever opposite to the side having the probe; and a laser. It includes a light source that emits a beam, a beam irradiation means that makes the laser beam incident on the reflecting surface of the cantilever at a predetermined angle, and a light receiving element that receives the reflected laser beam reflected by the reflecting surface. It is equipped with an optical lever sensor that has detection means for detecting and detecting the displacement of the probe based on this, and the light source is fixed, and the light receiving element and cantilever are movably supported for optical adjustment. Probe microscope. 2. The scanning probe microscope according to claim 1, wherein the cantilever is supported by a parallel spring having a contact surface for biaxially moving cantilever attachment. 3. The scanning probe microscope according to claim 1, wherein the detection means includes a convex lens arranged between the light receiving element and the cantilever.