JPH1151947A - Cantilever for scanning probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly vibrate a cantilever in response to the surface shape of a sample and observe the accurate shape by forming a through hole reducing the resistance received at the time of vibration on the vibrating portion of the cantilever. SOLUTION: When the whole of a cantilever 10 is thoroughly soft and the cantilever 10 is vibrated so that only its tip section is bent, a through hole 14 is formed at the tip section of the cantilever 10. The through hole 14 is provided near the tip section where vibration is generated while the strength of the tip section of the cantilever 10 is secured. When the cantilever 10 is vibrated, the atmospheric air, various gas, or a solution in the atmosphere passes through the through hole 14, and the resistance is sharply reduced. Since the gas or solution can be moved through the through hole 14 and the resistance is sharply reduced, the cantilever 10 correctly responds to the surface shape of a sample, and the surface shape of the sample can be correctly observed or measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cantilever for a scanning probe microscope, and more particularly to a structure of a cantilever for a scanning probe microscope represented by a scanning atomic force microscope (AFM). For example, the present invention relates to a cantilever for a scanning probe microscope that reduces the air damping effect when observing the shape of a sample surface by vibrating a wide cantilever.

[0002]

2. Description of the Related Art In recent years, a scanning atomic force microscope (AFM) used for elucidating an atomic structure or the like uses a cantilever having a probe at a tip as a scanning probe. In a scanning atomic force microscope using such a cantilever, an attractive force or a repulsive force based on an atomic force is generated between the sample surface and the probe by scanning the tip of the probe with the surface of the sample, The shape of the sample surface can be measured by detecting the atomic force as the amount of bending of the cantilever. And the amount of bending of the cantilever is, for example, by irradiating a laser beam on the back surface of the cantilever,
The displacement was measured by optically detecting the displacement of the reflected beam.

As the above-mentioned conventional cantilever, a relatively wide plate is used. This requires irradiating a laser beam to the back surface of the cantilever in order to detect the amount of bending of the cantilever, and requires a certain reflection area (width of the cantilever) to obtain the reflected beam.

The cantilever bends and vibrates based on the atomic force between the sample surface and the probe. However, in order to secure time response during the vibration, it is necessary to obtain a certain degree of rigidity and restoring force. Required a certain width.

[0005]

However, in such a conventional cantilever for a scanning probe microscope, the probe is scanned over the surface of the sample using a cantilever of a fixed width provided with a probe at the tip. When detecting the amount of bending of a cantilever due to an attractive force or a repulsive force based on an atomic force generated between a sample surface and a probe, if the cantilever is wide, it vibrates like a fan (particularly, vibrates in a dynamic mode). As a result, the lever surface receives air resistance (water resistance in the case of underwater), making it impossible to vibrate according to the surface shape of the sample, making it impossible to accurately observe the shape of the sample surface. Was.

In order to reduce air resistance during vibration of the cantilever, it is conceivable to employ a thin cantilever structure. However, when the width of the cantilever becomes narrow, lateral blur occurs easily at the time of vibration, and the cantilever is bent. There is a disadvantage that the laser beam that has been irradiated to detect the amount deviates from the irradiation position.

In addition, when the width of the cantilever is reduced,
Because the rigidity reduces the resilience during vibration,
There is a disadvantage that the time response of the cantilever deteriorates, and accurate shape observation and measurement of the sample surface cannot be performed.

The present invention has been made in view of the inconveniences of the prior art, and reduces the air resistance and the like when the cantilever vibrates, so that the cantilever is appropriately vibrated according to the shape of the sample surface, and accurate. It is an object of the present invention to provide a cantilever for a scanning probe microscope capable of performing various shape observations.

[0009]

In order to achieve the above object, in a cantilever for a scanning probe microscope according to the present invention, a cantilever provided with a probe at its tip and supported at a cantilever is used as a scanning probe. In a cantilever for a scanning probe microscope that scans the surface of a sample to detect the shape of the surface of the sample, a through hole is formed in a vibrating portion of the cantilever so as to reduce a resistance received when vibrating.

According to this, a through hole is formed in the vibrating part of the cantilever provided with a probe at the tip used in the scanning probe microscope to reduce the resistance during vibration.
Even if the working atmosphere is in the air, various gases, or solutions, the gas (including the atmosphere) and the solution can move through the through holes when the cantilever vibrates, greatly reducing the resistance received by the cantilever. it can. Therefore,
The cantilever vibrates accurately according to the sample surface shape, and it is possible to perform accurate observation and measurement of the sample surface shape.

[0011] In the cantilever for a scanning probe microscope according to the next invention, the side wall of the through-hole has a tapered shape to reduce the resistance received when the cantilever vibrates.

According to this, the shape of the side wall of the through hole of the cantilever is not formed parallel to the vibration direction of the cantilever, but is formed into a tapered shape with a constant inclination, so that when the cantilever vibrates, The resistance of the fluid (the use atmosphere of the cantilever is gas or solution) moving through the through hole can be further reduced. Therefore, the resistance when the cantilever vibrates is further reduced, and the cantilever can be vibrated accurately according to the sample surface shape, and the sample surface shape can be observed and measured more accurately.

In the cantilever for a scanning probe microscope according to the next invention, the outer peripheral side wall portion of the cantilever has a tapered shape for reducing the resistance received when the cantilever vibrates.

According to this, the outer peripheral side wall portion of the cantilever is not formed parallel to the vibration direction of the cantilever, but is formed into a tapered shape having a constant inclination, so that when the cantilever vibrates, the fluid ( Gas or solution)
The resistance inside can be further reduced. Therefore, the resistance when the cantilever vibrates is further reduced, and the cantilever can be vibrated accurately according to the sample surface shape, and the sample surface shape can be observed and measured more accurately.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a cantilever for a scanning probe microscope according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a plan view of a cantilever 10 for a scanning probe microscope according to the present embodiment, and FIG.
FIGS. 3A and 3B show a diagram of the cantilever 10 that can maintain the strength of the tip portion, FIG. 3A is a plan view of the tip portion of the cantilever 10, and FIG. 3A and 3B are views of the cantilever 10 for performing twist detection, wherein FIG. 3A is a plan view of the tip of the cantilever 10 and FIG. 3B is a view showing the motion of vibration of the tip of the cantilever 10. .

In this embodiment, the present invention is embodied as a cantilever 10 for a scanning probe used in a scanning atomic force microscope (AFM).
Is intended for use in the atmosphere, various gases, and solutions. The scanning atomic force microscope generates an atomic force between the probe 12 provided at the tip of the cantilever 10 and the sample surface (not shown) in these use atmospheres,
By scanning the cantilever 10 and detecting the degree of bending at each position, the fine surface shape of the sample is observed.

First, as shown in FIG. 1, when the entire cantilever 10 is sufficiently soft and vibrates so that only the tip end of the cantilever 10 is bent, the cantilever 1
0 is formed so that the through hole 14 is located at the front end.
The target cantilever has a hardness of 0.1 N / m or more.
This is the case of 5 N / m.

The number of through holes 14 to be formed in the cantilever 10 is not necessarily five as shown in FIG. 1 since the strength varies depending on the size and shape of the cantilever 10, but basically it is not necessary. Is to leave a laser beam reflecting surface 16 for detecting the amount of displacement at least at the tip 1/3 of the length of the cantilever 10, and otherwise provide a beam (such as a shoji). At present, the area of the reflection surface 16 needs to be at least 10 × 10 μm or more. Of course, if the cantilever is of a self-detection type that can detect the amount of deflection of the lever without using a laser beam, it is not necessary to secure the reflection surface 16.

The shape of the through-hole 14 formed in the cantilever 10 shown in FIG. 2A is such that the tip of the cantilever 10 does not break even when the probe 12 vibrates in a direction perpendicular to the plane of the paper. And normal vibration (Fig. 2
(B) in the vertical direction shown in FIG. 4B) is a case where the strength is given to such an extent that twisting does not occur. That is, FIG.
As shown in (a), the through-hole 14 formed near the tip of the cantilever 10 has three relatively thick beams 18 at the tip of the cantilever 10 because two holes are arranged at intervals. Can be supported.

As described above, in the cantilever 10 shown in FIG. 2, since the through hole 14 is provided in the vicinity of the tip where vibration is generated while maintaining the strength of the tip, the cantilever 10 is not exposed to the atmosphere when the cantilever 10 vibrates. The atmosphere, various gases or solutions pass through the through holes 14 and the resistance is greatly reduced.

Further, as shown in FIG. 3A, the shape of the through-hole 14 formed in the cantilever 10 is such that the width of the through-hole 14 is made large by using one through-hole 14 and two narrow beams 20. The tip of the cantilever 10 is supported. The reason why the beam 20 is formed thin is as follows.
As shown in FIG. 3B, this is because the torsion detection is performed by the probe 12.

Although not shown, for example, in the case where the cantilever 10 shown in FIG. 1 is hard and the entire lever vibrates, a through hole is formed over the entire surface of the cantilever 10 so that the resistance to vibration can be reduced. Can be reduced. In this case, the typical hardness of the cantilever 10 is 20 N / m to 100 N / m, but a cantilever having a higher hardness may be used. In this case as well, it is necessary to design in such a manner that the strength is adjusted in consideration of the torsion of the lever in accordance with the application as described above.

When a cantilever having a hardness (5 N / m to 200 N / m) which is in the middle of the above two examples is used, the position of the through hole 14 is also enlarged to about 1/2 of the length of the lever. The number of through holes 14 is also an intermediate number.

FIG. 4 is a view of the cantilever in which the side wall of the through hole 14 formed in the cantilever 10 is perpendicular to the lever surface, and FIG. 4A is a bottom view as viewed from the probe 12 side. And (b) are perspective views thereof. FIG.
3A is a view of a cantilever in which a side wall of a through hole 14 formed in the cantilever 10 has a taper 22 formed in an oblique direction with respect to the lever surface, and FIG. 3A is a bottom view as viewed from the probe 12 side. FIG. 2 (b) is a perspective view thereof.

In the present embodiment, as shown in FIG. 4, the through hole 14 formed in the cantilever 10 has a side wall perpendicular to the lever surface. As shown in FIG. 2, the side wall of the through hole 14 is tapered so that the side wall is inclined with respect to the lever surface.
May be provided.

As described above, the through hole 1 of the cantilever 10
As for the shape of the side wall portion of 4, the resistance is not the smallest when formed in the direction perpendicular to the lever surface, but the taper having various angles and sizes depending on the use atmosphere (gas or liquid) of the cantilever. It is desirable to form it and make it the side wall shape that minimizes the resistance. In FIG. 5, the taper 22 is formed such that the side wall of the through hole 14 is widened toward the probe 12 side.

For the same reason that the taper 22 is formed on the side wall of the through hole 14, the outer peripheral side wall of the cantilever 10 is also tapered 24 (see FIG. 6) or a taper 26 (see FIG. 7). FIG.
7 and FIG. 7, a through hole is not shown in order to explain the taper at the outer peripheral side wall portion of the cantilever 10, but a through hole is further formed in this embodiment.

As described above, the cantilever 10 for the scanning probe microscope according to the present embodiment is configured, and a manufacturing method for forming the cantilever 10 having these shapes will be described below.

First, as shown in FIGS. 1 to 4,
When forming the through-hole 14 having a side wall portion perpendicular to the lever surface of the cantilever 10, the shape to be punched is transferred to the substrate by using a photolithography technique in a semiconductor process, and a mask for forming the hole is formed. Is formed, and an etching process is performed using dry etching or wet etching, thereby forming the cantilever 10 and simultaneously forming the through hole 14 therein.

Various etching conditions such as an etching gas used for dry etching differ depending on a material to be etched (a material of a cantilever). In the case of performing wet etching, various conditions such as a kind of an etchant and a temperature and a concentration thereof are used. Will be different. However, the basic steps up to the formation of the etching mask are common to both dry etching and wet etching.

Therefore, a typical step of forming a cantilever will be described with reference to FIG. First, a silicon oxide film (SiO 2) 32 serving as an etching mask is formed on a substrate (here, Si) 30 by thermal oxidation or the like (see FIG. 8A). A photoresist is applied on the silicon film 32 by a spinner, and the shape of the mask is transferred and developed by photolithography to form a mask using the resist 34 (see FIG. 8B).

Third, the opening of the resist 34 is removed by etching with BHF (buffered hydrofluoric acid solution) in order to selectively remove the underlying silicon oxide film 32 by using the mask made of the resist 34 (see FIG. 2). FIG. 8 (c)).
Fourth, the through hole 14 and the cantilever 10 are simultaneously formed by etching away only the portion where the substrate (Si) 30 is exposed, using the portion where the resist 34 and the silicon oxide film 32 remain as an etching mask. (See FIG. 8D).

The steps up to the formation of the etching mask described above are common to both dry etching and wet etching. The etching method used in the substrate etching step is dry etching or wet etching. Either of the etchings can be used.

FIGS. 9A to 9D show FIGS.
3A to 3D are external views of cantilever forming steps corresponding to the respective steps.

The case where the etching step in FIG. 8D is performed by dry etching will be described. When the silicon substrate 30 is dry-etched using a reactive ion etching (RIE) apparatus, the etching conditions differ depending on whether the etched shape is tapered or not.

For example, as shown in FIG. 4, when the side wall of the through-hole 14 of the cantilever 10 is made perpendicular to the lever surface, SF6 and O2 are used as reactive gases in order to perform anisotropic etching. , Or a mixed gas of CHF3 or the like, and vertical etching is performed by utilizing the ion bombardment effect and by utilizing the wall effect of re-attaching the separated component of the resist to the wall surface.

As shown in FIG. 5, the cantilever 1
In the case where the taper 22 is formed in the 0 through-hole 14, only SF6 may be used as a reactive gas for performing isotropic etching, and the etching mask does not need to be a resist. Therefore, only the silicon oxide film 32 may be used. In this case, the etching does not use the ion bombardment effect but uses the reaction at the interface with the gas.

The case where the etching step in FIG. 8D is performed by wet etching will be described with reference to FIGS. First, in FIG. 8C,
The resist 34 is removed, leaving only the silicon oxide film 32,
On the back side of the substrate (Si) 30, a protective coat film 36 is formed to protect it from being etched when wet etching is performed (see FIG. 10). This protective coating film 3
For 6, a polyimide, a silicone resin, a fluorine compound synthetic rubber, or the like can be used as a substance having chemical resistance. Then, the protective coat film 36 covers a portion to be protected from wet etching. Further, in the present embodiment, the protective coat film 36 is used, but it is also possible to use a jig to protect the back surface of the substrate 30 from being etched.

Second, as shown in FIGS. 11 and 12, an aqueous solution of KOH, TMAH, EPW or the like is used as an etchant for performing anisotropic wet etching. In particular, as shown in FIG.
When it is desired to vertically etch the wall surface of the cantilever (the through hole 14 or the outer peripheral wall surface), the above-described etchant is used and the Si plane orientation of the silicon substrate 30 is changed to (11).
0).

As shown in FIG. 13, as an etchant for isotropic wet etching, a mixed solution of (hydrofluoric acid + nitric acid + acetic acid) or the like can be used in addition to a hydrofluoric acid aqueous solution. Note that a hydrofluoric acid solution can be used even when the etching material is silicon oxide (SiO 2) or quartz. By immersing the substrate 30 partially protected by the protective coat film 36 using such an etchant, isotropic etching is performed so that the shape of the through hole 14 becomes a desired shape (taper). .

FIGS. 6, 7, 13, and 1 show the case where the outer peripheral side wall of the cantilever 10 is tapered.
4 will be described. The taper treatment of the outer peripheral side wall of the cantilever 10 is the same as the above-described taper treatment of the through hole, and the outer peripheral side wall of the lever can be tapered by performing isotropic etching during dry etching. That is, in the isotropic dry etching, the etching proceeds on the side surface by the same length as the etching amount, and therefore, the taper 24 (see FIG.
) And the taper 26 (see FIG. 7). However,
The aspect ratio of the etching progress can be easily selected according to the etching conditions.

As described above, when wet etching is used, anisotropic etching is performed, and the side surface is basically formed in a tapered shape unless the crystal orientation is set to be vertical. Note that when performing isotropic wet etching as shown in FIG. 13, the length (v) of the protruding portion of the silicon oxide film 32 serving as an etching mask,
Height (h) of silicon substrate 30 and etching ratio (A)
You can ask for the relationship. FIG. 14 shows this relationship.

As described above, according to the present embodiment, by forming a through hole in a portion where the cantilever vibrates (especially, a tip portion), a fluid (gas or liquid) in an atmosphere in which the cantilever is used can be removed. This makes it possible to greatly reduce the resistance to be received, to accurately detect the movement of the probe that vibrates according to the surface shape of the sample, and to measure the shape appropriately.

Further, according to the present embodiment, the through hole of the cantilever and the outer peripheral side wall of the cantilever are tapered, so that the resistance of the cantilever to the fluid (gas or liquid) in the working atmosphere is greatly reduced. This makes it possible to accurately detect the movement of the probe that vibrates according to the surface shape of the sample, and perform appropriate shape measurement. In particular, the resolution in the dynamic mode in which the cantilever is vibrated during observation with a scanning atomic force microscope (AFM) can be greatly improved.

The present invention is not limited to the above-described embodiment. For example, a cantilever of a scanning atomic force microscope (AFM) is, as shown in FIG. In the case of the comparative example in which the through-hole is not opened, as shown in FIG.
When viewed from above, the tip position of the probe 12 is not visible.
Although it was impossible to position the tip positions of the probe 2, if the through hole 14 is formed as in the present embodiment, the tip position of the probe 12 can be confirmed through the through hole 14. It has the advantage of easy alignment

As an application of the present invention, as shown in FIG. 17, a sample 44 is scanned by using a lever 40 in which a through hole 42 is formed. At this time, on the surface of the sample 44, the reflection portions 46 and the non-reflection portions 48 are alternately arranged at regular intervals. Here, the surface of the sample 44 is irradiated through the through hole 42 of the lever 40, and the reflected light reflected on the surface can be received again. Using this device, the lever 40 is scanned on the sample surface, and the light reflection state and the non-reflection state are detected, and counted by a counter or the like, thereby measuring the length of a minute part or absorbing light. An image of reflection can be obtained.

Further, as shown in FIG. 17, in addition to detecting light reflected on the sample 44 by projecting light from above, FIG.
As shown in FIG. 5, the amount of absorption or reduction of the light transmitted through the sample 58 is determined by the photodetector 5 disposed on the back side of the lever 50.
4 and a photodetector 56 for detecting light passing through the through-hole 52
The measurement may be performed by providing In addition,
The light detection sensitivity can be varied by changing the shape and dimensions of the through holes 42 and 52 described above.

Further, as shown in FIG.
By incorporating a photodetector 64 such as a photodiode in the vicinity of the back surface side of the lever 60 on which the light source 2 is formed, the scattered light of the light applied to the surface of the sample 66 is detected by the photodetector 64, and the extremely fine area is detected. Can be detected. In addition, a reflected image can be obtained by using the photodetector 64.

Further, as an application of FIG. 19, FIG.
As shown in (1), by forming a lattice-shaped through-hole 72 in the lever 70, light interference is generated, and the length measurement can be performed in the same manner as described above by using the interference fringes.

Further, as shown in FIG.
The silicon oxide film (S
A thin film 84 such as iO2) or a polymer film is adhered (a similar structure may be formed while forming a hole, leaving only the film), and the thin film 84 is irradiated with light to bend the thin film 84. A photodetector 86 that detects reflected light that changes depending on the condition is provided, and a change in fluid pressure (air pressure, water pressure, etc.) can be detected.

Further, it can be used as a mask for a lithography or processing tool in a very small area. That is, as shown in FIG. 22A, a light-shielding film is formed by forming a through hole 92 in the lever 90 or by vapor deposition (or sputtering or the like) on a transparent lever such as silicon oxide. To form a light-shielding pattern (transfer pattern). As shown in FIG. 22 (b), when light is dropped from above, the lever 90 just serves as a mask, and when scanning is performed, the trajectory remains as a pattern (see FIG. 22 (d)).

When a photosensitive material such as a photoresist is used for the substrate, the pattern remains as a pattern of photosensitive marks. This allows lithography or processing of very small areas. As shown in FIG. 22C, by providing the fine probe 94 on the lever 90, the distance between the lever 90 and the substrate 96 can be controlled to the same level as in an atomic force microscope. Of course, in addition to leaving a scan mark by forming a pattern on the lever, batch exposure and processing using a stepper (step and repeat exposure apparatus) can be performed. In the case of processing, a laser such as YAG can be used. As a mask material at that time, a mask having good selectivity with the material to be processed is required.

[0054]

As described above, according to the cantilever for a scanning probe microscope according to the present invention, the through-hole provided in the cantilever can be used even when the cantilever is used in the atmosphere, various gases, or a solution. Since the gas and the solution can be moved through the channel and the resistance is greatly reduced, the cantilever responds accurately according to the sample surface shape, and the sample surface shape can be accurately observed or measured.

According to the cantilever for a scanning probe microscope according to the next invention, since the shape of the side wall of the through hole of the cantilever is tapered so as to have a constant inclination, the resistance of the cantilever when vibrating is further reduced. Thus, the cantilever can respond accurately according to the sample surface shape, and the sample surface shape can be observed or measured more accurately.

According to the cantilever for a scanning probe microscope according to the next invention, the shape of the outer peripheral side wall of the cantilever is tapered so as to have a constant inclination.
The resistance received when the cantilever vibrates is further reduced, so that the cantilever can respond accurately according to the sample surface shape, and the sample surface shape can be observed or measured more accurately.

[Brief description of the drawings]

FIG. 1 is a plan view of a cantilever for a scanning probe microscope according to the present embodiment.

FIG. 2 is a diagram of a cantilever capable of maintaining the strength of a tip.

FIG. 3 is a diagram of a cantilever capable of performing twist detection.

FIG. 4 is a view of a cantilever in which a side wall portion of a through hole formed in the cantilever is perpendicular to a lever surface.

FIG. 5 is a view of a cantilever in which a side wall of a through hole formed in the cantilever is tapered in an oblique direction with respect to a lever surface.

FIG. 6 is a diagram showing a cantilever having a tapered outer peripheral side wall portion.

FIG. 7 is a diagram showing a cantilever having a tapered outer peripheral side wall portion.

FIG. 8 is a process cross-sectional view illustrating a typical process of forming a cantilever.

FIG. 9 is an external view illustrating a typical step of forming a cantilever.

FIG. 10 is a cross-sectional view of a substrate on which a mask for performing wet etching is formed.

FIG. 11 is a sectional view of a cantilever in which a tapered through hole is formed by performing anisotropic wet etching.

FIG. 12 is a cross-sectional view of a cantilever in which a through hole perpendicular to the lever surface is formed by performing anisotropic wet etching.

FIG. 13 is a process sectional view of a cantilever in which a tapered through hole is formed by performing isotropic wet etching.

FIG. 14 is a diagram illustrating an etching ratio when performing isotropic wet etching.

FIG. 15 is a diagram showing a cantilever of a comparative example.

FIG. 16 is a diagram showing a cantilever according to the present embodiment.

FIG. 17 is a diagram illustrating another application example of the cantilever according to the present embodiment.

FIG. 18 is a diagram illustrating another application example of the cantilever according to the present embodiment.

FIG. 19 is a diagram illustrating another application example of the cantilever according to the present embodiment.

FIG. 20 is a diagram illustrating another application example of the cantilever according to the present embodiment.

FIG. 21 is a diagram illustrating another application example of the cantilever according to the present embodiment.

FIG. 22 is a diagram illustrating another application example of the cantilever according to the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Cantilever 12 Probe 14 Through hole 16 Reflecting surface 18, 20 Beam 22, 24, 26 Taper

Claims (3)

[Claims] 1. A cantilever for a scanning probe microscope which scans a sample surface by using a cantilever supported by a cantilever provided with a probe at a tip portion as a scanning probe to detect a shape of the sample surface, wherein a vibration portion of the cantilever vibrates. A cantilever for a scanning probe microscope, characterized in that a through hole is formed to reduce the resistance that is sometimes applied. 2. The cantilever for a scanning probe microscope according to claim 1, wherein a side wall of the through hole has a tapered shape to reduce a resistance received when the cantilever vibrates. 3. The cantilever for a scanning probe microscope according to claim 1, wherein an outer peripheral side wall of the cantilever has a tapered shape to reduce a resistance received when the cantilever vibrates.