JPH04179042A - Cantilever for scanning probe microscope - Google Patents

Abstract

PURPOSE:To obtain a cantilever suited for a scan-type probe microscope in which a displacement-measuring device using a heterodyne method is incorporated, by equipping the cantilever with a flexible cantilever portion having a sharply edged probe at its tip end, a support portion for supporting the cantilever portion, and a reference portion provided at a position spaced, at a specified distance, from that tip end. CONSTITUTION:The cantilever has a flexible cantilever portion 14 having a sharply edged probe 12 at its tip end and elastically deformable when the probe 12 receives a force, a support portion 16 for supporting the cantilever portion 14, and a reference portion 22 provided at a position spaced, at a specified distance, from a tip end portion of the cantilever portion 14. Namely, the reference portion 22 used as a reference when detection is made of the movement of the cantilever portion 14 at a tip end thereof is provided at a position spaced, by a specified distance, from this tip end independently of the length of the cantilever portion 14. Therefore, even when the cantilever is applied to a displacement-measuring device using a heterodyne method incapable of changing the beam interval d, at all times the measuring beams are irradiated onto the tip end portion of the cantilever portion 14 while a reference beam onto the reference portion 22. This enables obtaining a cantilever applicable to a scan- type probe microscope with an optical system for measuring the displacement by the heterodyne method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cantilever for a scanning probe microscope. In particular, the present invention relates to a flexible cantilever that is easily elastically deformed in response to a weak force and is used as a force detection element in an atomic force microscope or a magnetic force microscope.

[Prior art] Binnig and Rohrer
The scanning tunneling microscope invented by
Tunneling Microscope (STM)
) by using elemental technologies such as servo technology,
An atomic force microscope (8FM) has been proposed as a device that can observe the surface shape of an insulating sample with atomic-order accuracy, which could not be measured using TM. When two atoms (or molecules) are brought very close together, there is an IQ of -19 to 10 between them.
As the name suggests, an atomic open force microscope is a device that uses atomic force to observe the surface shape of a sample, and a force (atomic force) of about -12 [N] is applied.The probe is supported by a flexible cantilever. Then, the tip is brought close to the sample surface until the tip of the cantilever is displaced to some extent by the atomic force acting on the atoms at the tip of the tip, and the tip is scanned along the sample surface while keeping this amount of displacement constant. During scanning, when a change in the displacement of the cantilever corresponding to the unevenness of the sample surface is detected, a fine movement mechanism such as a piezoelectric element is used to move the cantilever closer or further away from the sample surface by the corresponding amount to bring it back to the initial value. As a result, the tip of the probe draws a curved surface that reflects the unevenness of the sample surface. Therefore, it is possible to obtain a three-dimensional image showing the surface shape of the sample from the voltage applied to the piezoelectric element.

[Problems to be Solved by the Invention] Various displacement measurement methods can be applied to the method of detecting the displacement of the cantilever. One of them is an optical displacement measurement method called the heterodyne method. In the heterodyne method, a light beam from a light source is split into two light beams using a Wallaston prism or the like, and one of the light beams (measurement light beam Lm) is sent to the tip of the cantilever 14, as shown in FIG. 11A. (measurement point), and the other light beam (reference light beam Lr) is irradiated to the fixed end of the cantilever 14 (reference point) near the support part 16, and by interfering with these reflected lights, The movement of the measurement point is measured as relative movement. This heterodyne method is effective when measuring the movement of the cantilever part with respect to a reference point while exciting and modulating the probe using a piezoelectric element or the like.

For example, an example of a scanning probe microscope that incorporates the heterodyne method into a cantilever displacement measurement system is disclosed in Japanese Patent Application No.
It is shown in Japanese Patent No. 28332.

Generally, in a scanning probe microscope, cantilevers with different mechanical resonance frequencies and spring constants are used depending on the measurement conditions and measurement sample. The resonant frequency and spring constant of a cantilever are determined by the properties and mechanical shape of the material that makes up the cantilever. To create cantilevers with different resonance frequencies and spring constants, changing the mechanical shape rather than changing the material of the cantilever is often done, since this can be done without changing the manufacturing process.

However, cantilevers whose characteristics are changed by changing the mechanical shape, particularly the length of the cantilever, have the following disadvantages when measuring displacement using the heterodyne method. The distance between the two light beams used in the heterodyne method is determined by the characteristics of the Wollaston prism and the numerical aperture of the condensing lens, and cannot be adjusted depending on the length of the cantilever.

Therefore, when using a long cantilever, the 11th B
As shown in the figure, since the measurement light beam is irradiated to the middle of the cantilever 14, only about half the displacement of the tip of the cantilever can be detected.On the other hand, if a short cantilever is used, the reference beam is irradiated to the middle of the cantilever 14. The light beam is connected to the support part 1
This is undesirable in design because it causes an optical path difference between the two light beams.Furthermore, since the support part is quite thick, when the focusing position of the measurement light beam is aligned with the cantilever surface, the support The reference light beam irradiated onto the area becomes out of focus, making accurate measurement impossible.

In this way, conventionally there has been no cantilever suitable for displacement detection using the heterodyne method.

An object of the present invention is to provide a cantilever suitable for a scanning probe microscope equipped with an optical system that measures displacement using the heterodyne method.

[Means for Solving the Problems] A cantilever for a scanning probe microscope according to the present invention includes a displacement measurement system that measures the displacement of the tip with respect to the reference by irradiating light onto the tip of the cantilever and the reference. A cantilever used in a scanning probe microscope, which has a sharp tip at its tip, has a flexible cantilever part that deforms elastically when the probe receives force, and a support part that supports the cantilever part. , and a reference part provided at a position a predetermined distance from the tip of the cantilever part.

[Function] In the cantilever according to the present invention, the reference portion, which serves as a reference for detecting the movement of the tip portion of the cantilever portion, is provided at a predetermined distance from the tip portion, regardless of the length of the cantilever portion. Therefore, even when applied to a displacement measurement system using a heterodyne method in which the beam interval cannot be changed, the measurement light beam always irradiates the tip of the cantilever part, and the reference light beam always irradiates the reference part. Therefore, cantilever sections with different lengths (characteristics) can be used without adjusting the displacement measurement system.

[Example] Hereinafter, a cantilever according to an example of the present invention will be described with reference to the drawings.

The cantilever IO according to the present invention, whose perspective view is shown in FIG. 1A and its I-1 sectional view is shown in FIG. 1B,
Triangular cantilever section 14 with a probe 12 at its tip
and a plate-shaped support portion 16 that supports this. The cantilever portion 14 is integrally formed with the fixed portion 1.
8 is fixed to the bottom surface of the support portion 16. A rectangular opening 20 is provided in the support portion 16, and a reference portion 22, which is a part of the fixed portion 18, is exposed. This opening 20 is provided at a position where the distance between the tip of the cantilever portion 14 and the center of the reference portion 22 is equal to the beam distance d of the displacement measurement system using the heterodyne method.

Figures 28 to 2C show how a displacement measurement system using the terodyne method is applied to a cantilever 10 having cantilever portions 14 of three different lengths. Now, cantilever part 1
4 and the center of the reference portion 22 is always a constant distance d regardless of the length of the cantilever portion 14.
When the reference light beam Lr is irradiated onto the reference section 22, the measurement light beam Lm is ideally irradiated onto the tip of the cantilever section 14 in either case. Therefore, there is no need to make any adjustments to the displacement measurement system when using cantilevers with different spring constants and the like.

Such a cantilever 10 can be manufactured by applying a semiconductor IC manufacturing process. The present inventors actually produced the cantilevers shown in FIGS. 1A and 1B. Hereinafter, the manufacturing method will be explained with reference to FIGS. 3A to 3D. First, 100 Si wafers ((100
) After cleaning the Si wafer 10 by thermal oxidation.
A 5 in 2 film 102 was formed on the substrate 0 to a thickness of LO [nm]. 6 Then, a resist material 104 was coated and exposed in a circular shape of 5 μmφ as a probe pattern using a mask aligner. After the development process, the Si02 film 102 and the S1 wafer 100 were etched using the remaining resist material 104 as a mask by anisotropic plasma etching using SF6 and CIF as etching gases (FIG. 3A), removing the remaining Si posts. 106 was slightly tilted due to the presence of the resist material 104. Thereafter, the resist material 104 and the Sto2 film 102 were removed and further plasma etching was performed. As shown in FIG. 3B, sharp protrusions 108 are formed on the Si wafer 100. As shown in FIG.・112 was formed. Next, after coating the 5-in2 film 112 on the lower surface with a resist material, a pattern for forming the cantilever part and the opening was formed by photolithography, and using this pattern as a mask, an anisotropic Si film was prepared using a potassium hydroxide aqueous solution. 5 inches on the top surface by etching
The unmasked portion was etched until the second film 110 was exposed.

Second viscosity A cantilever section 10 was fabricated as shown in Figure 3D. Note that the opening was formed to have a size of 250 [μm] square.

In the cantilever lO manufactured in this way, since the constituent materials of the cantilever part 14 and the reference part 22 are both 5 in2, the reflection bands of both are equal, and the amount of reflected light of the light beam irradiating the cantilever part 14 and the reference part 22 is This has the advantage of eliminating the need for correction. Of course, in order to improve the S/N ratio of the displacement measurement system, a light reflective metal film such as gold can be provided on the cantilever section 14 and the reference section 22.

As mentioned above, when producing cantilevers from Si wafers using the semiconductor IC process, one type of cantilever may be produced from one Si wafer, but as shown in Fig. 4, one Si wafer It is also possible to fabricate several types of cantilevers 10 having cantilever portions 14 of different lengths at the same time. In this case, there is an advantage that it is not necessary to prepare the number of exposure masks corresponding to the length of the cantilever portion. This figure shows the top view of a Si wafer 100 on which 18 cantilevers 10 having three different lengths of cantilevers 114 have been fabricated. Although the position of 22 does not reflect the actual dimensions, the distance between the reference portion 22 of each cantilever 10 and the tip of the cantilever portion 14 is always a constant value d.

Next, another type of cantilever is shown in FIGS. 5A and 5B.
This will be explained with reference to the figures. FIG. 5A is a perspective view of the cantilever, and FIG. 5B is a cross-sectional view taken along the line v--2. The cantilever 10 in this example is the same as the one described above except for the shape of the opening 20 provided in the support portion 16. . In this example,
The opening 20 is not rectangular but is opened toward the cantilever section 14. For this reason, a reference portion 22 is formed continuously on the upper surface of the cantilever portion 14 . Note that the width of the opening 20 can be made narrower than the width of the fixed end of the cantilever 14 in order to bring the vibration mode of the cantilever 14 as close as possible to an ideal cantilever as shown in FIG. 1A. preferable.

3, each having a cantilever portion 14 of a different length.
6A to 6C show how a displacement measurement system using the heterodyne method is applied to a type of cantilever 10. Similar to the type of cantilever described above, a measurement light beam LL1 and a reference light beam are used. L" is ideally irradiated to the tip of the cantilever section 14 and the reference section 22. Therefore, there is no need to adjust the displacement measurement system when replacing cantilevers with different characteristics.

Such a cantilever 10 was produced using the same method as the above-mentioned cantilever. The only difference is that when patterning the cantilever section 14 and the reference section 22 using a photoringraph in the final step, a mask open to the cantilever side is used as a mask for the reference section 22. As a result, the shape of the fixed end of the cantilever portion 14 is changed due to anisotropic etching of Si using an aqueous potassium hydroxide solution.
The opening did not form a perfectly right angle, but instead had a shape that widened toward the cantilever portion 14. However, the cantilever was suitable for a displacement measurement system using the heterodyne method.

Still another type of cantilever is shown in FIG. 7. In this cantilever 10, three cantilever parts 14 of different lengths are provided on one support part 16. If we pay attention to one pair of cantilever part 14 and reference part 22, its structure is the same as that of two cantilevers in FIG.
The distance between the tip of each set of cantilever sections 14 and the center of the reference section 22 is a constant distance d. Therefore, as shown in FIGS. 2A to 2C, the measurement light beam Lm and the reference light beam Lr are each coupled to a cantilever beam.
The distal end of the section 14 and the center of the reference section 22 are irradiated,
It can be applied to displacement measurement systems using the heterodyne method without requiring adjustment. Note that during measurement, the cantilever section 14 other than the necessary cantilever section 14 is removed.

Each length is 80 (:μm・120[μlll]・
Such a cantilever 10 having three cantilever portions 14 of 160 [μal] was produced in the same manner as shown in FIGS. 3A to 3D. At this time, the distance d from the tip of the cantilever section 14 to the center of the reference section 22 is 800 μm1, and the size of the reference section 22 is 200 μm1.
[I made it to μI. During the measurement, the unused cantilever section 14 was broken off and removed so as not to interfere with scanning.

The cantilever thus produced was also suitable for a scanning probe microscope incorporating a heterodyne displacement measurement system.

Yet another type of cantilever is shown in FIG. 8. In this example, the reference portion 22 is formed into an elongated rectangle, and its long side is the length of the longest cantilever 14 and the length of the shortest cantilever portion 14. It is longer than the difference between S and S. Due to this.

A distance d can be ensured between the tip of any cantilever section 14 and the reference section 22.

Another embodiment of the cantilever according to the present invention is shown in FIG. 9A.The reference part is preferably strong against external mechanical vibrations.

It is permissible as long as it does not affect the displacement detection of the displacement measurement system, but the less the better.To achieve this, it is necessary to increase the thickness of the reference part and set the mechanical resonance frequency to a high frequency side. It is valid. Cantilever 1 of this example
0 was created in accordance with this principle, and is provided with a reference portion 22 that integrally protrudes from the support portion 16 so as to cover a portion of the cantilever portion 14. The reference part 22 is formed thicker than the cantilever part 14, and its mechanical resonance frequency is set higher than that of the cantilever part 14. Thereby, the reference part 22 satisfies the above-mentioned conditions. In addition, the reference section 22 is provided at a distance d from the tip of the cantilever section 14. As a result, the measurement light beam LI11 is directed to the tip of the cantilever section 14 by the reference light beam, similar to the above-described embodiment. The reference portion 22 is irradiated with the beam Lr. Moreover, the reference part 22 is located at a position lower than the upper surface of the support part 16 so that the spot shape of the reference light beam focused thereon is not significantly different from that of the measurement light beam focused on the tip of the cantilever part 14. is integrally formed. When producing cantilever portions 14 of different lengths, this is done by changing the length k of the portion covered by the reference portion 22 while keeping the distance from the tip to the reference portion 22 constant. Note that the height difference between the cantilever section 14 and the reference section 22 varies depending on the sample to be measured and the measurement method of the scanning probe microscope;
It is desirable to set it to about [nm] or several tens [nm], bs, L2! However, this value does not limit the invention in any way.

An example of a cantilever 10 having a plurality of cantilever parts 14 having different lengths is shown in FIG. 9B.The distance from the tip of any cantilever part 14 to the reference part 22 is the same, and The length of the covered part is different. To create a cantilever with a similar function, it is possible to modify the support side of the cantilever so that the roots are aligned, but the configuration shown in this figure is better.

The cantilever of the present invention can be easily produced because the volume of the portion to which fine buttering is applied is small.

Still another embodiment of the cantilever according to the present invention is shown in FIG. 10. The cantilever 10 of this embodiment is similar to the example shown in FIG. 5B in the cantilever portion 14, probe 12, support portion 16, etc. The manufacturing process is different. The support part 16 is made by pasting glass, and the cantilever part 14
and the reference part 22 is silicon nitride, and the lower part 24
is made of silicon. The glass of the support part 16 is.

It is bonded to silicon or silicon nitride using an anodic bonding method. The cantilever IO in this example is the reference part 2.
2 has the advantage of being extremely resistant to external vibrations. Note that the cantilever 10 is constructed by constructing the support portion 16 with silicone and the reference portion 22 or the lower portion 24 with glass.
It is possible to create both. Cantilever 10 like this
When the reference part 22 is attached to a scanning probe microscope for measurement, the lower part 24 of the reference part 22 is thick, so the reference part 22 is attached at an angle with respect to the sample.

Next, a manufacturing method actually performed by the present inventors will be explained.

First, after cleaning the S1 wafer, CVD Si and N4
150 [nm] was deposited by using a potassium hydroxide aqueous solution, and in order to make a probe part as a replica of the Si etching trace, a 5 [μm] square hole was made in the Si and N4 by photolithography, and then the Si was etched using a potassium hydroxide aqueous solution. 6 Next, after removing Sj, N, by plasma etching, Si was re-etched.
, N4 was deposited to a thickness of 500 [nm] over the entire surface including the square pyramid-shaped holes by CVD. And further 1100℃
Annealing in water vapor to slightly reduce 3102 to S
After attaching it to N4, the cantilever shape and other shapes were exposed and patterned using photolithography.

On the other hand, Pyrex glass (Corning $77
40) before anodic bonding to the above Si wafer.

A groove for cutting the cantilever, a groove to prevent Pyrex glass from sticking to the cantilever part, and a groove for the opening of the reference part were machined with a dicing saw. 3. Next, what Si wafer and Pyrex glass should be cut first? They were joined by anodic bonding, and a groove was cut with a dicing saw from the side opposite to the groove in which the cantilever part was first attached, and the individual pieces were separated to complete the cantilever.

As described above, since the cantilever is manufactured using a semiconductor IC manufacturing process, semiconductor materials such as Si and compounds derived from it are often used as materials for forming the cantilever. The support portion, the reference portion, and the like may be fabricated by bonding glass or the like to Si using anodic bonding, and glass or the like is often used as a material constituting the cantilever of the present invention.

Since the displacement of the cantilever and reference part is captured optically, the reflectance of light at each part is important as it affects the measurement accuracy. Therefore, it is preferable to apply a reflective coating to the cantilever and the reference part.

Although the cantilever of the present invention is suitably used in a scanning probe microscope incorporating a displacement measurement system using the heterodyne method, the present invention is not limited to the method of such a displacement measurement system. If it is a method in which the cantilever part and the reference part are each irradiated with a light beam created by dividing the emitted light beam into multiple parts, or with multiple light beams emitted from multiple light sources, and the relative positional changes between the two are captured, It can be applied well not only to the heterodyne method.

[Effects of the Invention] According to the present invention, a cantilever suitable for a scanning probe microscope incorporating a displacement measurement system using a heterodyne method can be provided. That is, even if cantilevers of different lengths are used to select and measure the mechanical resonance frequency or spring constant, the scanning probe microscope can be used without making any adjustments. Therefore, the time required for adjusting the device before measurement can be extremely shortened, and measurement data can be obtained in a short time. In addition, since the cantilever of the present invention is manufactured by applying a semiconductor IC process, it can be manufactured with high precision on the order of μm and with excellent reproducibility, and can be manufactured at a low cost by using a batch process. can be provided.

[Brief explanation of drawings]

FIG. 1A is a perspective view of a cantilever according to an embodiment of the present invention, FIG. 1B is a sectional view taken along line I-1 of the cantilever in FIG. 1A, and FIGS. 2A to 2C are views of FIGS. 1A and 1B. Figures 3A to 3D are diagrams illustrating the method for manufacturing the cantilevers shown in Figures 1A and 1B. , FIG. 4 is a diagram showing how a plurality of cantilevers shown in FIGS. 1A and 1B are formed on one 51 wafer, and FIG. 5A is a perspective view of another type of cantilever. Figure 5B is a v-v sectional view of the cantilever in Figure 5A, Figures 6A to 6C are the displacement measurement system using the terodyne method applied to the cantilever shown in Figures 5A and 5B. FIG. 7 is a diagram showing still another type of cantilever, FIG. 8 is a diagram showing still another type of cantilever, and FIGS. 9A and 9B are diagrams showing the cantilever of the present invention. FIG. 10 is a diagram showing still another embodiment of the cantilever of the present invention. FIGS. 11A to 11C are diagrams illustrating disadvantages that occur in the conventional cantilever. In the figure, 12 is a probe, 14 is a cantilever part, 16 is a support part, and 22 is a reference part. Applicant's representative Patent attorney Atsushi Tsuboi ■ Figure 1A Figure 18 Figure 2A Figure 128 Figure 1113A Figure 7-ko Figure 3B Figure 13c Figure 3D *1 + Figure ■ Figure 5A Figure 58IIA 6AtA 11168 Figure l6c55 No. 7uA Figure 8 @ Figure 9A Figure 98 1i10tlA 11th Arl! J J11118rlA I111CtJA

Claims (1)

[Claims] A cantilever used in a scanning probe microscope equipped with a displacement measurement system that measures the displacement of the tip with respect to the reference by irradiating light onto the tip of the cantilever and the reference, the cantilever having a sharp point. a flexible cantilever part that has a probe at its tip and deforms elastically when the probe receives force; a support part that supports the cantilever part; and a position a predetermined distance away from the tip of the cantilever part. A cantilever for a scanning probe microscope, comprising a reference part provided at the cantilever.