JP2016063280A - Manufacturing method of micromachine vibration structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to improve a Q-value of a micro-vibrator in use under a practical environment.SOLUTION: The manufacturing method of a micromachine vibration structure includes: forming a vibration structure composed of an atomic layer material capable of constituting in an atomic layer unit such as graphene on a substrate in a step S101, and making a fluorine compound gas to act on the vibration structure. For instance, a vibration structure made of graphene may be exposed in a XeFgas in a step S102.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for manufacturing a micro mechanical vibration structure made of an atomic layer material such as graphene.

  In recent years, since various microphysical quantities can be detected with high sensitivity, research and development of micromechanical vibrators have been actively conducted as constituent elements of NEMS (Nanoelectro mechanical systems) sensors. For example, in the case of mass measurement (Non-Patent Document 1), the minimum detection amount of a minute physical quantity depends on the lightness of the vibrator structure and its resonance characteristic (Q value). For this reason, in order to achieve more sensitive sensing, lightening of the vibrator structure and high Q value are being promoted.

In terms of weight reduction, in recent years, graphene and silicene (graphene-like substances in which silicon forms crystals in a honeycomb lattice), h-BN, MoS ₂ , RuO _2, etc. are used as the structural material of the vibrator. Attention has been paid. For example, graphene is a material that has excellent mechanical properties and is extremely lightweight, and can be expected as a structural material of a vibrator sensor.

  However, the Q value of graphene vibrators operating at room temperature is generally low (Non-Patent Document 2, Non-Patent Document 3), and it is necessary to improve the Q value in order to achieve high-sensitivity sensing. As a method for improving the Q value, there is a report of a high Q value graphene vibrator operating in a cryogenic environment (Non-Patent Document 4).

K. L. Ekinci et al., "Ultrasensitive nanoelectromechanical mass detection", Applied Physics Letters, vol.84, no.22, pp.4469-4471, 2004. J. S. Bunch et al., "Electromechanical Resonators from Graphene Sheets", Science, vol.315, pp.490-493, 2007. S. Shivaraman et al., "Free-Standing Epitaxial Graphene", Nano Letters, vol.9, no.9, pp.3100-3105,2009. Y. Xu et al., "Radio frequency electrical transduction of graphene mechanical resonators", Applied Physics Letters, vol.97, 243111, 2010.

  However, the above-described increase in the Q value using the cryogenic temperature is not practical as a technique for increasing the Q value in consideration of the industrial use in a normal environment of room temperature of the graphene vibrator. For this reason, a technique for improving the Q value of an oscillator using an atomic layer material such as graphene in a normal environment of room temperature is demanded.

  The present invention has been made to solve the above problems, and an object of the present invention is to improve the Q value of a fine vibrator when used in a practical environment.

The manufacturing method of the micro mechanical vibration structure according to the present invention includes a first step of forming a vibration structure made of an atomic layer material that can be configured in units of atomic layers on a substrate, and a fluorine compound gas in the vibration structure. A second step to act. In the first step, a vibration structure made of graphene is formed on the substrate, and in the second step, XeF ₂ gas may be applied to the vibration structure.

  As described above, according to the present invention, since the fluorine compound gas is allowed to act on the vibration structure, the Q value of a fine vibrator (vibration structure) can be improved by use in a practical environment. An excellent effect is obtained.

FIG. 1 is a flowchart illustrating a method for manufacturing a micromechanical vibration structure according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing the state of each step for explaining a method for manufacturing a micromechanical vibration structure in an embodiment of the present invention using graphene as an atomic layer material. FIG. 3 is a scanning electron micrograph of the graphene vibrator. FIG. 4 is a characteristic diagram showing the result of measuring the resonance characteristics of the graphene vibrator. FIG. 5 is a perspective view showing a configuration example of a micro mechanical vibration structure to which the present invention is applicable. FIG. 6 is a perspective view showing a configuration example of a micro mechanical vibration structure to which the present invention is applicable. FIG. 7 is a perspective view showing a configuration example of a micro mechanical vibration structure to which the present invention is applicable. FIG. 8 is a perspective view showing a configuration example of a micro mechanical vibration structure to which the present invention is applicable. FIG. 9 is a perspective view showing a configuration example of a micro mechanical vibration structure to which the present invention is applicable.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart illustrating a method for manufacturing a micromechanical vibration structure according to an embodiment of the present invention.

  In this manufacturing method, first, in step S101, a vibration structure made of an atomic layer material that can be configured in units of atomic layers such as graphene is formed on a substrate. For example, if a support is formed on a substrate and a beam portion having one end fixed to the support is formed of an atomic layer material, a cantilever vibration structure can be obtained.

Next, in step S102, a fluorine compound gas is allowed to act on the vibration structure. For example, a vibration structure made of graphene may be exposed to XeF ₂ gas.

  Next, it demonstrates in detail using an Example. Below, the result of producing a membrane type vibration structure (graphene vibrator) using graphene by using graphene as an atomic layer material will be described.

First, as shown in FIG. 2A, a resist pattern 203 was formed on a SiO ₂ layer 202 having a thickness of 280 nm on a silicon substrate 201. The resist pattern 203 includes an opening 204. The SiO ₂ layer 202 can be formed by thermally oxidizing the surface of the silicon substrate 201. Further, as described below, a resist pattern 203 may be formed by a known lithography technique.

  For example, ZEP-520A (manufactured by Nippon Zeon Co., Ltd.), which is an electron beam resist, is applied by spin coating to a thickness of 600 nm to form a resist film, and 180 ° C. for 1 minute to remove the solvent, etc. Heat treatment is performed under the following conditions.

Next, the resist film is exposed using a well-known electron beam exposure technique, and then developed to form a resist pattern 203 having an opening 204. The acceleration voltage of the electron beam used for electron beam exposure may be 50 kV, the beam current may be 1 nA, and the exposure amount may be 150 μC / cm ² . In the developing step, o-xylene may be used as a developing solution, and IPA (Isopropyl alcohol) may be used as a rinsing solution.

Next, as shown in FIG. 2B, the resist pattern 203 is used as a mask, CHF ₃ and O ₂ mixed gas is used as an etching gas, and the SiO ₂ layer 202 is subjected to reactive ion etching (RIE). Then, an opening 205 was formed. In this etching process, the CHF ₃ gas flow rate was 50 sccm, and the O ₂ gas flow rate was 3 sccm. Note that sccm is a unit of flow rate, and indicates that a fluid at 0 ° C. and 1013 hPa flows 1 cm ³ per minute. The etching time was 30 minutes.

Next, the resist pattern 203 was removed by RIE using O ₂ gas. In RIE using this O ₂ gas, the O ₂ gas flow rate was 20 sccm, the pressure was 1 Pa, the RF power was 500 W, and the bias power was 38 W. The processing time was 1 minute.

Next, as shown in FIG. 2C, a silicon substrate 201 is wet etched using a TMAH (Tetramethylammonium hydroxide) etching solution “Pure Etch 160” (manufactured by Hayashi Junyaku Co., Ltd.) and using the SiO ₂ layer 202 as a mask. Thus, the trench structure 206 was formed. Here, the temperature of the etching solution was 65 ° C., and the etching time was 10 minutes.

Next, as illustrated in FIG. 2D, the graphene 207 is disposed so as to be installed at the end of the opening 205, and a membrane-type graphene vibrator using the graphene 207 is manufactured. For example, graphene may be grown on a Cu foil by a CVD (Chemical Vapor Deposition) method, and the graphene may be transferred. For example, graphene formed on a Cu foil is peeled off using a PMMA (Polymethyl methacrylate) film. Next, the graphene attached to the PMMA film is disposed (attached) on the SiO ₂ layer 202 (opening 205). Thereafter, if the PMMA film is dissolved with acetone, the graphene 207 to be installed in the opening 205 can be formed.

Next, as shown in FIG. 2E, XeF ₂ gas was allowed to act on the graphene 207 to perform fluorination surface modification on the graphene 207. For example, using a XeF ₂ gas etching apparatus (BP-3F, SAMCO), graphene 207 was exposed to XeF ₂ gas for 30 seconds in the processing chamber of this apparatus. After this treatment, it has been confirmed that the fluorine atom 208 is bonded to each carbon atom of the graphene 207.

  FIG. 3 shows the result of observation of the graphene vibrator thus produced with a scanning electron microscope. FIG. 3 is a scanning electron micrograph of the produced graphene vibrator. FIG. 3B is an enlarged view of a part of FIG. It can be seen that a membrane-type graphene vibrator having a dimension in plan view of about 2 μm × 2 μm is formed.

Next, the results of evaluating the resonance characteristics of the graphene vibrator described above will be described. Resonance characteristics were evaluated using an optical heterodyne vibrometer. In this evaluation, first, a substrate on which a graphene vibrator is manufactured is placed on the stage of the sample chamber of the optical heterodyne vibrometer, and the sample chamber is evacuated to a vacuum degree of 10 ⁻² Pa. In this state, using a semiconductor laser with an oscillation wavelength of 408 nm, the graphene vibrator on the substrate was vibrated (excited) by the optical excitation method, and the resonance characteristics were measured. The laser used for the resonance characteristic measurement is a 632.8 nm He—Ne laser. The temperature of the resonance characteristic measurement environment was room temperature.

  The measurement results described above are shown in FIG. FIG. 4 is a characteristic diagram showing the result of measuring the resonance characteristics of the graphene vibrator. FIG. 4A shows a resonance characteristic measurement result before fluorination surface modification of a single-layer graphene vibrator having a dimension in plan view of 2 μm × 2 μm. FIG. 4B shows a resonance characteristic measurement result after modification of the fluorinated surface of a single-layer graphene vibrator having a dimension in plan view of 2 μm × 2 μm.

  As shown in FIG. 4A, the Q value of the graphene vibrator before the fluorination surface modification is 354. In contrast, as shown in FIG. 4B, the Q value of the graphene vibrator after the fluorination surface modification is 2722, and the Q value is improved by about 7.7 times by applying the fluorination surface modification. It will be done.

As described above, the Q value can be improved by performing surface modification using XeF ₂ gas, which is a fluorine compound gas, on the graphene vibrator, which is a carbon-based atomic layer material. In addition, this manufacturing method can be implemented by a very simple process, and has high affinity with existing semiconductor manufacturing process technology, MEMS (Micro Electro Mechanical Systems), and NEMS manufacturing process technology. As described above, the present invention is considered to be applicable to various element research and development and manufacturing using a vibrating structure made of an atomic layer material such as graphene.

  By the way, the micro mechanical vibration structure may be composed of a cantilever beam 502 supported by a support body 501 as shown in FIG. Moreover, as shown in FIG. 6, you may comprise from the support body 501 and the beam 502 of the both ends supported by the support body 503. Moreover, as shown in FIG. 7, you may comprise from the circular membrane by the thin film 505 formed on the support body 504 which has circular opening.

  Further, as shown in FIG. 8, the micromechanical vibration structure may be configured by both free end vibration portions 508 supported by connection support structures 506 and 507 that connect the support body 501 and the support body 503. Moreover, as shown in FIG. 9, it is good also as a structure which connected the two beams 509 and 510 of the both ends supported by the support body 501 and the support body 503 by the connection structure 511,512. As described above, the shape of the micro mechanical vibration structure can be variously modified and applied based on the gist of the present invention.

  As described above, according to the present invention, since the fluorine compound gas is allowed to act on the vibration structure made of the atomic layer material, the Q value of a fine vibrator (vibration structure) can be used in a practical environment. Can be improved. A micro mechanical vibrator is an element that is expected to be a key component in the production of sensors, arithmetic circuits, and the like due to its high-speed response characteristics and high sensitivity characteristics, and is being researched and developed. In the production of next-generation devices using such micromechanical vibrators, a technique for improving the dynamic characteristics (particularly the Q value) of the micromechanical vibrators is an important elemental technology. Among them, graphene having extremely lightweight characteristics and excellent mechanical properties is a material expected as a structural material for the mechanical element. According to the present invention that can improve the dynamic characteristics (Q value) of a graphene vibrator in a normal environment of room temperature (room temperature), it may become an important elemental technology for realizing the next-generation device described above.

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious. For example, in the above description, graphene produced by the CVD method is used. However, the present invention can also be applied to an element in which graphene produced by a technique such as a tape peeling method or thermal decomposition of SiC is used as a vibration structure. In the above description, graphene is exemplified as the atomic layer material. However, the present invention is not limited to this, and the same applies to carbon-based materials such as carbon nanotubes.

  In addition, the formation of the micro mechanical vibration structure is to use a combination of multiple existing ultra-fine processing technologies such as electron beam exposure technology, photolithography, nanoimprint technology, dry / wet etching technology, vapor deposition / sputtering / chemical vapor deposition. But it is possible. The formation of a vibration structure using an atomic layer material or a micro mechanical vibration structure on the order of nano / micrometers is not limited to the above description. In addition, although surface modification using a gas atmosphere has been exemplified, the same effect can be expected by using a surface modification technique such as photochemical surface reaction, use of low energy ions, or surface coating.

201 ... silicon substrate, 202 ... SiO ₂ layer, 203 ... resist pattern, 204 ... opening, 205 ... opening, 206 ... trench structure 207 ... graphene, 208 ... fluorine atom.

Claims (2)

A first step of forming on the substrate a vibration structure made of an atomic layer material that can be configured in units of atomic layers;
And a second step of causing a fluorine compound gas to act on the vibration structure. In the method for producing a micro mechanical vibration structure according to claim 1,
In the first step, a vibration structure made of graphene is formed on a substrate,
In the second step, a XeF ₂ gas is allowed to act on the vibration structure.