JP6989091B2 - Diamond Structures, Diamond Cantilever, and Methods for Manufacturing Diamond Structures - Google Patents

Description

The present invention relates to nano- and micro-electromechanical system devices and the like, and particularly to single crystal tiremond structures that can be used as core elements of such devices.

Sensor devices and signal processing devices are becoming more sophisticated, smaller, portable and wearable, and cantilever and resonators using MEMS (Micro Electro Electrical System) and NEMS (Nano Electro Electrical System) as core elements to support them. The demand for higher precision is increasing.
One of the important performance indexes of the MEMS / NEMS cantilever and the resonator is the quality factor Q, and technological development for obtaining a high quality factor (high Q value) is constantly being promoted.

Diamond has many notable properties such as high Young's modulus, highest hardness, high thermal conductivity, hydrophobic surface, and excellent corrosion resistance. For this reason, diamond is a near-ideal material that realizes a MEMS / NEMS cantilever and resonator with higher quality factors than existing materials such as silicon.

Previous studies on MEMS / NEMS using diamond have been mostly polycrystalline (PCD), nanocrystal (NCD), and ultra-nanocrystal diamond (UNCD) grown on dissimilar substrates (Patent Reference 1). And see Non-Patent References 1 and 2).
However, since the grain boundaries and sp2 components act on these diamonds, the performance required for MEMS / NEMS cannot be fully achieved. For example, thermoelastic loss is an energy loss inherent in MEMS / NEMS, which is a determinant of device quality factors, but in these diamonds thermoelastic loss is inadequate, not at the level of diamond single crystals. It is a thing.

On the other hand, single crystal diamond (SCD) has extremely low elastic loss and thermal elastic loss. Therefore, it is considered that the use of SCD for MEMS / NEMS cantilever and resonator is more suitable than the use of PCD, NCD and UNCD.

As a MEMS using a single crystal diamond, an SCD resonator produced by a diamond-on-insulator (DOI) method has been reported (see Non-Patent Document 3). However, since the diamond MEMS in this DOI method is bonded to a different type of substrate, there is a problem that the quality factor is lowered based on the difference in the coefficient of thermal expansion between the diamond and the substrate. Further, in the case of application under a high temperature such as 600 ° C., the MEMS / NEMS bonded to the dissimilar substrate has a problem of deterioration in reliability.
Further, as disclosed in Patent Document 2, the present inventors have invented an SCD cantilever using an ion implantation assisted lift-off (IAL) method. However, the quality factor of the SCD cantilever (mechanical resonator) by this method remained at the level of 1000.

U.S. Patent Application Publication No. 2010/0055806 Japanese Unexamined Patent Publication No. 2011-168460

Microelectromech. System. , Vol. 24, p. 2152 (2015) J. Micromech. Microeng. , Vol. 19, p. 115016 (2009) Apple. Phys. Let. , Vol101, p. 163505 (2012)

The problem to be solved by the present invention is to provide a diamond structure having extremely high quality factors and little deterioration in performance even at high temperatures, and a method for manufacturing the same, by utilizing the excellent properties of single crystal diamond. It is to be.
Specifically, MEMS / NEMS cantilever and mechanical resonators with extremely low elastic loss and thermal elastic loss, little deterioration in performance even at high temperatures such as 600 ° C, and extremely excellent quality factors of 500,000 or more. It is to provide mechanical resonators and methods for their manufacture.

The configuration of the present invention is shown below.
(Structure 1)
In a diamond structure in which a diamond beam is formed on a single crystal diamond layer via a support portion.
The beam consists of a surface defect layer and a body layer.
The surface defect layer is made of diamond-like carbon and is made of diamond-like carbon.
The thickness of the surface defect layer is 2% or less with respect to the thickness of the main body layer.
The main body layer is a diamond structure made of single crystal diamond.
(Structure 2)
The diamond structure according to configuration 1, wherein the support portion contains graphite.
(Structure 3)
The diamond structure according to configuration 1 , wherein the support portion is made of graphite.
(Structure 4)
The diamond structure according to configuration 1, wherein the support portion includes diamond.
(Structure 5)
The diamond structure according to any one of configurations 1 to 4, wherein the thickness of the surface defect layer is 1% or less with respect to the thickness of the beam.
(Structure 6)
The diamond structure according to any one of configurations 1 to 4, wherein the thickness of the surface defect layer is 0.2% or less with respect to the thickness of the beam.
(Structure 7)
The diamond structure according to any one of configurations 1 to 6, wherein the beam is a cantilever.
(Structure 8)
A diamond cantilever having the structure of the diamond structure according to any one of configurations 1 to 7.
(Structure 9)
A substrate preparation process for preparing a substrate having a single crystal diamond layer formed on at least a part of the surface,
An ion implantation step of forming a graphite-like carbon damaged layer in the single crystal diamond layer by implanting ions from the surface side of the substrate on which the single crystal diamond layer is formed.
The first heat-treated with forming a diamond epitaxial layer on a surface of the single crystal diamond layer, and the first of the graphite-like carbon damage layer Graphite modified layer to the diamond epitaxial layer forming step by heat treatment When,
A high-quality crystallization heat treatment step of applying a second heat treatment to the diamond epitaxial layer to reduce crystal defects of diamond, and
An etching mask forming step of forming an etching mask for forming a beam on the diamond epitaxial layer, and an etching mask forming step.
And dry etching step for processing to form the beam dry etching is performed until at least the Graphite modified layer reaches a depth,
A portion of the Graphite modified layer is removed by wet etching using a solution containing acid, and wet etching process for forming the beam,
A method for manufacturing a diamond structure, comprising: a defect layer etching step of etching at least a part of a defect layer formed on the beam in an oxygen atmosphere, and a method for manufacturing a diamond structure.
(Structure 10)
The method for manufacturing a diamond structure according to the configuration 9, wherein the substrate is a single crystal diamond substrate.
(Structure 11)
The method for manufacturing a diamond structure according to Configuration 9, wherein the substrate is a single crystal diamond substrate in which a single crystal diamond layer is epitaxially formed.
(Structure 12)
The method for manufacturing a diamond structure according to claim 9, wherein the substrate is a rigid substrate on which a single crystal diamond film is bonded.
(Structure 13)
The method for producing a diamond structure according to any one of configurations 9 to 12, wherein the defect layer etching step is performed under heat treatment conditions of 500 ° C. or higher and 1500 ° C. or lower.
(Structure 14)
The defect layer etching step, the oxygen partial pressure is carried out under 10 2 ^Pa or more 10 5 ^Pa or less environment, producing a diamond structure according to any one of the configurations 9 13.
(Structure 15)
The method for producing a diamond structure according to any one of configurations 9 to 14, wherein the heat treatment in the high-quality crystallization heat treatment step is performed under vacuum at 500 ° C. or higher and 1500 ° C. or lower.
(Structure 16)
The method for manufacturing a diamond structure according to any one of configurations 9 to 15, wherein the etching mask is made of metal.
(Structure 17)
The method for producing a diamond structure according to any one of configurations 9 to 15, wherein the wet etching is performed with an acid containing sulfuric acid.
(Structure 18)
The method for producing a diamond structure according to any one of configurations 9 to 17, wherein cleaning for removing organic substances and / or foreign substances is performed after the defect layer etching step.
(Structure 19)
The method for producing a diamond structure according to configuration 18, wherein the cleaning is performed by at least one selected from the group of hydrogen plasma, ozone, and oxygen plasma.

According to the present invention, a MEMS / NEMS cantilever and a mechanical resonator having extremely low elastic loss and thermal elastic loss, little deterioration in performance even at a high temperature such as 600 ° C., and an extremely excellent quality factor of 500,000 or more. And it becomes possible to provide mechanical resonators and their manufacturing methods.

Explanatory drawing which shows the structure of the cantilever using the single crystal diamond of this invention. (A) is a plan view, and (b) and (c) are sectional views. The process diagram which showed the manufacturing process of the cantilever using the single crystal diamond of this invention by the cross-sectional view of the main part. The process diagram which showed the manufacturing process of the cantilever using the single crystal diamond of this invention by the cross-sectional view of the main part. Sectional drawing which shows the structure of the substrate of this invention. The manufacturing flow diagram which showed the manufacturing process of the cantilever using the single crystal diamond of this invention. An optical micrograph of the diamond cantilever and resonator produced in Example 1 observed from above. An optical micrograph of the diamond cantilever produced in Example 1 observed from above. A characteristic diagram showing the vibration spectrum of a single crystal diamond cantilever. A characteristic diagram showing the relationship between the resonance frequency of a single crystal diamond cantilever and the length of a beam. A characteristic diagram showing the relationship between the resonance frequency of a single crystal diamond cantilever and atomic layer etching. A characteristic diagram showing the atomic layer etching time dependence of the quality factor of the produced single crystal diamond cantilever. A characteristic diagram showing an example of quality factor measurement by the ring-down method. A characteristic diagram showing the relationship between the thickness ratio of the defect layer and the quality factor. A mapping diagram in which quality factors are plotted with or without defect layer etching with the resonance frequency as a parameter. The characteristic figure which shows the resonance frequency characteristic at the measurement temperature 600 degreeC of the produced single crystal diamond cantilever.

First, the structure of the diamond structure of the present invention will be described.
As shown in FIG. 1, the diamond structure 101 of the present invention has a structure portion 12 made of a diamond single crystal, a support portion composed of a graphite modified layer 13 and a defect layer 14, and at least on the surface thereof. It is composed of a substrate 11 on which a single crystal diamond layer is formed. The structure portion 12 is composed of a beam portion 12a and a support portion 12b. Here, the support portion composed of the graphite modified layer 13 and the defect layer 14 contains graphite and diamond, but it can also be made of graphite.
1 (a) is a plan view, FIG. 1 (b) is a cross-sectional view taken along the plane connecting A and A'of FIG. 1 (a), and FIG. 1 (c). 1 (a) shows a cross-sectional view when a cross section is taken at the plane connecting B and B'in FIG. 1 (a).

In this diamond structure 101, the quality factor Q when the beam portion 12a is resonated includes various factors such as air damping, loss derived from the support portion, beam portion (beam portion) bulk loss, beam portion surface loss, and thermoelastic loss. It decreases under the influence of various factors.
Therefore, these factors were analyzed in detail.
As a result, it was found that the defect layer 14b was formed on the lower surface of the exposed portion of the beam portion 12a, and the defect layer 14b lowered the quality factor Q.

The defect layer 14b has a Young's modulus substantially the same as that of the structure portion 12 made of single crystal diamond, and is a thin layer that is not removed even by wet etching when processing the graphite modified layer 13 described later. Since the defect layer 14b has almost the same Young's modulus as the structure portion 12, the existence of the defect layer 14b is difficult to infer from the resonance frequency. Further, in general, soft wet etching with a slow etching rate is less likely to damage the workpiece and less likely to form a defect layer. Further, since the defect layer usually has a faster etching rate for wet etching than the main body without defects, it is easy to remove the defect layer by performing wet etching. Further, since the place where the defect layer is formed is the back side of the structure portion 12 which is separated from the substrate 11 at a slight interval, it is difficult to analyze.
Under such circumstances, it was found as a result of detailed examination that the defect layer 14b reduces the quality factor Q.

As a result of further detailed analysis, the thickness of the defect layer 14b is 2% or less, preferably 1% or less, more preferably 0.02% or less with respect to the thickness of the structure portion 12 made of a diamond single crystal. It was found that the quality factor Q becomes significantly larger.
In the diamond structure 101 of the present invention, the thickness of the defective layer 14b of the exposed portion on the lower surface of the beam portion 12a is 2% or less, preferably 1% or less, based on the thickness of the structure portion 12 made of a diamond single crystal. , More preferably 0.02% or less.
This structure makes it possible to supply a diamond structure such as a cantilever having a high quality factor Q.

Further, in the above description, the case where the diamond structure 101 has a cantilever beam has been described, but the beam is not limited to the cantilever and can be a cantilever (bridge).
The cantilever structure is excellent in that it has a large amplitude and is easy to detect vibration, and that it is suitable for measurement with a probe needle attached to the end. Therefore, the cantilever structure is particularly suitable for cantilever.
On the other hand, the double-sided beam structure has the features of excellent strength and high durability.

<Manufacturing method>
Next, the method for manufacturing the diamond structure 101 of the present invention will be described with reference to FIGS. 2 to 5.

As shown in FIG. 5, which shows the process flow, the diamond structure 101 of the present invention is roughly divided into a mother body forming step C1, a shape forming step C2, and a defect removing step C3. The matrix forming step C1 includes a substrate preparation step S1, an ion implantation step S2 for forming a graphite-like carbon damaged layer, a step S3 for forming a diamond epitaxial layer and forming a graphite layer, and a heat treatment step S4 for improving crystal quality. Consists of. The shape forming step C2 includes an etching mask forming step S5, a dry etching step S6, and a wet etching step S7. The defect removing step C3 includes a defect layer etching step S8 and a cleaning step S9, and when the cleaning step S9 is completed, the diamond structure is provided and the process ends (S10).

The details of each step will be described below.

1. 1. Board preparation process (S1)
In the substrate preparation step S1, a substrate 11 having a single crystal diamond layer formed on at least a part of the surface is prepared (FIG. 2A). Here, FIG. 2 shows a cross-sectional view in each step. The left side of column (α) is the cross section when divided by the line connecting A and A'in FIG. 1 (a), and the right side of column (β) is B and B'in FIG. 1 (a). The cross section when divided by the line connecting is shown.
The substrate includes a single crystal diamond substrate 21 (FIG. 4 (a)), a substrate in which a single crystal diamond layer 22 is epitaxially formed on the single crystal diamond substrate 21 (FIG. 4 (b)), a Si wafer, and a polycarbonate. A substrate (FIG. 4 (c)) in which a single crystal diamond film 24 cut out by opening or the like is bonded onto a rigid substrate 23 such as a plastic substrate such as a substrate, a metal substrate such as an aluminum substrate, or a glass substrate such as a synthetic quartz substrate. )) And so on.
As the single crystal diamond layer, in addition to the non-doped single crystal diamond, a doped single crystal diamond to which nitrogen, boron, phosphorus or the like is added can also be used. Examples of the type of single crystal diamond include Ib type and IIa type. Further, as the plane orientation of the single crystal diamond layer, in addition to the (100) plane, any plane such as the (111) plane or the (110) plane can be used.

2. 2. Ion implantation step (S2)
High-energy ion implantation is selectively performed on the surface of the single crystal diamond substrate 11a to form a graphite-like carbon damaged layer in the diamond layer. More specifically, high energy ion implantation is performed to form a graphite-like carbon damaged layer 13a in the diamond layer 11 as shown in FIG. 2 (b). At this time, the defect layer 14a is also formed in the diamond layer 11 in contact with the graphite-like carbon damaged layer 13a.
Examples of the ion type for ion implantation include boron ion (B ⁺ ), carbon ion (C ⁺ ), and hydrogen ion (He ⁺ ). The ion energy is 180 keV or more and 1 MeV or less, and the beam current is 180 nA /. Examples include cm ² or more and 500 nA / cm ² or less, an injection angle of 0 ° or more and 7 ° or less, and an injection amount of 1 × 10 ¹⁶ pieces / cm ² or more and 5 × 10 ¹⁶ pieces / cm ² or less.
After ion implantation, the surface is cleaned by cleaning. For this cleaning, for example, a mixed acid solution consisting of nitric acid and hydrofluoric acid can be used.

3. 3. Diamond epitaxial layer forming step (S3)
In this step, the diamond epitaxial layer 15 is grown on the single crystal diamond layer 11 (FIG. 2 (c)).
As a method for forming the diamond epitaxial layer 15, a microwave plasma vapor deposition (MPCVD) method can be mentioned.
The film thickness of the diamond epitaxial layer 15 may be appropriately determined, and examples thereof include 0.2 μm and more and 5 μm or less.

Examples of the raw material gas for MPCVD include methane (CH ₄ ), and examples of the carrier (diluted) gas include hydrogen (H ₂ ). Examples of the film forming conditions include a CH ₄ flow rate of 0.4 sccm, a hydrogen gas flow rate of 500 sccm, a growing pressure of 10 KPa, a microwave power of 400 W, a substrate temperature of 960 ° C., and a growth time of 8 hours. Here, the thickness of the epitaxial layer 15 under this condition is about 0.3 μm.
Here, it is preferable that the supply of methane gas is stopped after the growth is completed, and then the temperature is maintained at the substrate temperature in a hydrogen atmosphere to bring the surface of the diamond epitaxial layer 15 into a hydrogen-terminated state.

Then, a mixed acid solution treatment is performed to remove the surface conductive layer, and the surface of the diamond epitaxial layer 15 is used as an oxygen termination layer. Examples of the mixed acid solution include a mixed acid solution composed of sulfuric acid and nitric acid. For example, a treatment is performed at 300 ° C. for 60 minutes in a mixed acid solution having a volume ratio of sulfuric acid: nitric acid = 1: 1.

By the heat treatment in this diamond epitaxial layer forming step, the graphite-like carbon damaged layer 13a formed in the single crystal diamond layer 11 by ion implantation is changed to the graphite modified layer 13b.

4. Heat treatment step (S4)
Samples are annealed under high vacuum to reduce defects in the diamond epitaxial layer 15 and the single crystal diamond layer 11.
The annealing temperature is preferably 500 ° C. or higher and 1500 ° C. or lower. Below 500 ° C., annealing is insufficient and defects in the diamond epitaxial layer 15 and the single crystal diamond layer 11 cannot be sufficiently reduced, and as a result, the quality factor Q of the produced sample is sufficiently high. It is not possible. If the temperature exceeds 1500 ° C., problems such as easy cracking in the diamond epitaxial layer 15 and the single crystal diamond layer 11 are likely to occur. As a typical processing temperature, 1100 ° C. can be mentioned.
The annealing time is preferably 1 hour or more and 10 hours or less. If it is less than 1 hour, it becomes difficult to sufficiently reduce the defects. Annealing for more than 10 hours is a waste of time and reduces manufacturing throughput. A typical annealing time is 6 hours.
The degree of vacuum is preferably 100 Pa or less. In particular, it is not preferable that an active substance or the like is in the environment. For example, when oxygen is in the environment, diamond is oxidatively etched.

5. Etching mask forming step (S5)
In the etching mask forming step (S5), an etching mask 17 for processing diamond is formed on the diamond epitaxial layer 15 (FIG. 3A).
Since the diamond is dry-etched with an oxygen-based gas, it is preferable that the etching mask 17 has dry etching resistance to the dry etching of the oxygen-based gas and can be removed by wet etching without etching the diamond.
For this reason, as the etching mask 17, metals such as aluminum (Al), gold (Au), titanium (Ti), and chromium (Cr) can be preferably used. Here, when Au is used, it is preferable to have a laminated structure in which a metal such as Ti that can be easily removed by wet etching is formed on the bottom side. Further, compounds such as tungsten carbide (WC) and hafnium carbide (HfC), and oxides such as alumina (Al ₂ O ₃ ) and silicon oxide (SiO _X ) can also be used.

In the etching mask 17, a processing film to be an etching mask is formed on the diamond epitaxial layer 15, a resist pattern is formed on the processing film by lithography, and the processing film is dry-etched using the resist pattern as an etching mask. It can be formed or it can be formed by the lift-off method.
For example, in the case of forming by the lift-off method, a resist pattern 16 is formed on the diamond epitaxial layer 15 (FIG. 2 (d)), and an Al (aluminum) film 17a is deposited by a vacuum vapor deposition method or a sputtering method (see FIG. 2 (d)). FIG. 2 (e)), the etching mask 17 made of Al can be formed by performing lift-off (FIG. 3 (a)). As the film thickness of the etching mask 17, for example, 300 nm can be mentioned.

6. Dry etching process (S6)
After that, as a dry etching step (S6), reactive ion etching using oxygen gas is performed to process the diamond layer. In this dry etching, etching is performed to a depth at which the bottom of the graphite modified layer 13b is removed (FIG. 3 (b)). Here, instead of reactive ion etching, focused ion beam etching or laser beam etching may be used.
Etching conditions for reactive ion etching using oxygen gas include, for example, O ₂ gas flow rate 90 sccm, high frequency power 800 W, bias power 20 W, and operating pressure 0.5 Pa. The etching rate of diamond under this condition is 60 nm / min.

7. Wet etching process (S7)
Then, wet etching is performed to etch the graphite modified layer 13b to form an element having a single crystal diamond-on-diamond substrate structure, for example, a cantilever or a bridge resonator (FIG. 3 (c)). The graphite modified layer 13 remaining by this wet etching becomes a component of the support portion of the beam.
Examples of the wet etching solution include an acid containing sulfuric acid, for example, a mixed acid composed of sulfuric acid and nitric acid. Here, in order to increase the etching rate, it is preferable to raise the temperature of the wet etching solution.

8. Defect layer etching step (S8)
Next, defect layer etching is performed to remove the defect layer exposed by the wet etching from the defect layer 14a. As a result, the defective layer 14 remains in the portion sandwiched between the graphite modified layer 13 and the single crystal diamond layer 11. The defect layer 14 in that portion becomes a part constituting the support portion (FIG. 3 (d)).
As a method of etching the defect layer, oxygen etching at a high temperature and in an oxygen environment can be mentioned.
Below 1500 ° C. 500 ° C. or higher as the temperature, the partial pressure of oxygen can be used in favor of less ¹⁰ 2 Pa or more ¹⁰ 5 Pa. If the temperature is lower than 500 ° C., the etching rate is extremely lowered, which is not preferable in terms of throughput. If the temperature exceeds 1500 ° C., problems such as easy cracking in the diamond epitaxial layer 15 and the single crystal diamond layer 11 are likely to occur, and etching uniformity and controllability are deteriorated. Further, the etching rate decreases extremely when the partial pressure of oxygen is below 10 2 ^Pa, the throughput is not preferable. Above the 10 5 ^Pa etch uniformity and controllability is degraded.
This high-temperature etching method under oxygen partial pressure has the characteristic that diamond is less likely to be broken, altered, or deformed even at high temperatures, so that it can be etched with almost no new defects generated by high-temperature treatment. preferable.

9. Cleaning process (S9)
Finally, cleaning is performed for the purpose of removing contamination by organic substances and the like.
As the cleaning method, a hydrogen plasma method, an ozone irradiation method, an oxygen plasma method and the like can be preferably used. Here, in a plasma method such as a hydrogen plasma method or an oxygen plasma method, a microwave plasma method, a radio frequency plasma method, a DC plasma method, or the like can be used.
For example, as conditions for hydrogen plasma treatment using microwave plasma, _{a flow rate of hydrogen gas (H 2} ) of 500 sccm, a pressure of 10 KPa, a microwave power of 800 W, and a substrate temperature of 800 ° C. can be mentioned.

<Making a diamond structure>
A cantilever and a bridge resonator were produced as a diamond structure. Hereinafter, the manufacturing process will be described with reference to FIGS. 2 and 3 which are cross-sectional views and FIG. 5 which shows the process flow.
1. 1. Board preparation process (S1)
As a substrate made of the single crystal diamond layer 11, a diamond substrate 11a having an Ib-type insulating (100) plane orientation was prepared (FIG. 2A). This substrate is made of high temperature and high pressure, and its size is 3 mm × 3 mm × 0.5 mm.

2. 2. Ion implantation step (S2)
High-energy ions were selectively implanted into the (100) plane surface of the single crystal diamond substrate 11a. The conditions are shown below.
Ion species: C ⁺
Ion energy: 180keV
Beam current: 180 nA / cm ²
Injection angle: 7 °
Injection volume: 1 x 10 ¹⁶ pieces / cm ²
By this ion implantation, a graphite-like carbon damaged layer 13a made of a graphite-like carbon layer was formed in a region at a depth of 0.5-1 μm from the substrate surface (FIG. 2 (b)). At this time, the defect layer 14a is generated in a part of the single crystal diamond layer 11 in contact with the upper surface of the graphite-like carbon damaged layer 13a.
Here, after ion implantation, the surface was washed in a mixed acid solution consisting of nitric acid and hydrofluoric acid (the volume ratio was nitric acid: hydrofluoric acid = 1: 1). The time of immersion in this mixed acid solution was 3 hours, and the treatment was carried out under boiling with a heater. After this washing, rinsing was performed under pure water with ion-exchanged water.

3. 3. Diamond epitaxial layer forming step (S3)
The diamond epitaxial layer 15 was grown on the single crystal diamond layer 11 by the microwave plasma vapor deposition (MPCVD) method (FIG. 2 (c)). The growth conditions are as follows.

Raw material gas: Methane (CH ₄ ), flow rate 0.4 sccm
Carrier (diluted) gas: hydrogen (H ₂ ), flow rate 500 sccm
CH ₄ / H ₂ flow rate ratio: 0.08%
Growing pressure: 10 KPa
Microwave power: 400W
Substrate temperature: 960 ° C
Growth time: 8 hours Thickness of epitaxial layer 15: 0.3 μm
Here, after the growth was completed, the supply of methane gas was stopped, and then the diamond epitaxial layer 15 was kept at the substrate temperature in a hydrogen atmosphere for 30 minutes. Therefore, the surface of the diamond epitaxial layer 15 is in a hydrogen-terminated state.

Then, a treatment at 300 ° C. for 60 minutes was performed in a mixed acid solution consisting of sulfuric acid and nitric acid (the volume ratio is sulfuric acid: nitric acid = 1: 1) to remove the surface conductive layer, and the surface of the diamond epitaxial layer 15 was oxygen-terminated. Layered.

By the heat treatment in this diamond epitaxial layer forming step, the graphite-like carbon damaged layer 13a formed in the single crystal diamond layer 11 by ion implantation is changed to the graphite modified layer 13b.

4. Heat treatment step (S4)
Samples were annealed in an ultra-high vacuum chamber to reduce defects in the diamond epitaxial layer 15 and the single crystal diamond layer 11. The annealing conditions are as follows.
Base pressure: 1x10 ^-8 Pa
Substrate temperature: 1100 ° C
Annealing time: 6 hours

5. Etching mask forming step (S5)
Next, a resist pattern 16 is formed on the diamond epitaxial layer 15 (FIG. 2 (d)), an Al (aluminum) film 17a is deposited by a vacuum vapor deposition method (FIG. 2 (e)), and then lift-off is performed. A metal mask 17 for etching made of Al having a film thickness of 300 nm was formed (FIG. 3A).

6. Dry etching process (S6)
After that, as a dry etching step (S6), reactive ion etching using oxygen gas was performed to process the diamond layer. In this dry etching, etching was performed to a depth at which the bottom of the graphite modified layer 13b was removed (FIG. 3 (b)).
The dry etching conditions are as follows.
O ₂ gas flow rate: 90 sccm
High frequency power: 800W
Bias power: 20W
Working pressure: 0.5Pa
Etching time: 60 minutes The etching rate of diamond at this time was 60 nm / min.

7. Wet etching process (S7)
After that, wet etching was performed in a mixed acid solution consisting of sulfuric acid and nitric acid boiled by a heater (the volume ratio is sulfuric acid: nitric acid = 1: 1) to etch the graphite modified layer 13b, and the single crystal diamond-on-diamond substrate was etched. A bridge resonator was formed with a cantilever having a structure (FIG. 3 (c)). The graphite modified layer 13 remaining by this wet etching becomes a component of the support portion of the cantilever.

8. Defect layer etching step (S8)
Next, the defect layer etching was performed under the conditions shown below to remove the defect layer exposed by the wet etching from the defect layer 14a. As a result, only the portion sandwiched between the graphite modified layer 13 and the single crystal diamond layer 11 remained in the defect layer 14, and that portion became a portion constituting the cantilever support portion (FIG. 3 (d)).
Atmosphere: O ₂
Atmospheric pressure: 20KPa
Substrate temperature: 500 ° C
Etching time: A sample was prepared by dividing it into 6 steps from 10 hours to 380 hours. The etching rate of diamond by this defect layer etching was 0.25 nm / h.

9. Cleaning process (S9)
Finally, hydrogen plasma treatment was performed by the microwave plasma vapor deposition (MPCVD) method for the purpose of removing contamination by organic substances and the like. The processing conditions are as follows.
Gas: Hydrogen (H ₂ ), flow rate 500 sccm
Pressure: 10KPa
Microwave power: 800W
Substrate temperature: 800 ° C
Growth time: 30 minutes Here, after the microwave was powered off, the sample was placed in a hydrogen gas atmosphere for 60 minutes to cool.

Through the above steps, a cantilever and a bridge resonator, which are diamond structure samples, were produced. The beam portion of the cantilever and the bridge resonator is composed of the single crystal diamond layer 11 and the diamond epitaxial layer 15, but since the diamond epitaxial layer 15 is sufficiently heat-treated, these beams are simply. It is in a state where it can be said that it is made of crystalline diamond. The supporting portion thereof is composed of a graphite modified layer 13 and a defect layer 14.
An optical micrograph of the cantilever and the bridge resonator prepared for reference is shown in FIG.
In the figure, 1 is a diamond substrate region. Reference numeral 2 is a region where ions are implanted, and beam (beam-shaped portion) 3 is a portion that becomes a cantilever. The beam 4 is a portion that becomes a bridge of the resonator.

FIG. 7 shows an optical microscope image of the finally produced cantilever. 5 in the figure is a diamond substrate region. 6, 7 and 8 are ion-implanted regions, of which 6 are connected to the diamond substrate at the support of the diamond beam. 7 and 8 are portions where the graphite modified layer is etched by wet etching to form an overhang shape. Of these, 8 is the part that becomes the beam of the cantilever. As can be seen from the figure, cantilever of various lengths were made.

<Characteristic evaluation>
(1) Resonance frequency spectrum FIG. 8 shows an example of the vibration frequency spectrum of a cantilever made of single crystal diamond after performing the defect layer etching and cleaning steps (after step S9). Here, the cantilever has a length of 100 μm, a width of 66 μm, and a thickness of 1.4 μm.
The vibration frequency spectrum was measured by placing a cantilever manufactured on the piezo element and driving the piezo element with a voltage. The spectrum analyzer used is a digital lock-in amplifier (manufactured by Zurich).
As a result, the resonance frequency of this cantilever was 432.56 KHz, and the quality factor Q was as high as 160,000. It was confirmed that the cantilever made of single crystal diamond produced by this technique resonates with an extremely high quality factor.

この共振周波数特性から、カンチレバー（単結晶ダイヤモンド・カンチレバー）のヤング率Ｅは１１０ＧＰａと計算された。なお、ｔはカンチレバーの厚さ、ρはカンチレバーの密度、ｋは係数である。 (2) Young's modulus FIG. 9 shows the relationship between the resonance frequency f of the manufactured cantilever and the length L of the cantilever. The resonance frequency f is Euler-Bernoulli shown in the following (Equation 1). The relationship of Bernoulli) was satisfied.

From this resonance frequency characteristic, the Young's modulus E of the cantilever (single crystal diamond cantilever) was calculated to be 110 GPa. In addition, t is the thickness of the cantilever, ρ is the density of the cantilever, and k is a coefficient.

(3) Etching rate of defect layer etching FIG. 10 shows the relationship between the resonance frequency of the cantilever and the defect layer etching time. As shown in FIG. 10A, when the time for etching the defect layer was extended, the resonance frequency of the cantilever decreased. For example, the resonance frequency was 484.358 kHz when the defect layer etching was performed for 10 hours, but changed to 432.560 kHz after the defect layer etching for 380 hours.
FIG. 10B shows how the resonance frequency changes with the time of etching the defect layer. From this change in resonance frequency, it is estimated that the thickness of the cantilever beam decreased by about 180 nm after etching the defect layer for 380 hours. Since the cantilever beam is etched from both the front and back sides, the etching rate of the defect layer etching was estimated to be about 0.25 nm / h.

(4) Quality factor Q
As shown in FIG. 11, 380 hours of defect layer etching significantly improved the quality factor calculated from the resonant frequency spectrum from 5000 to 160000.
FIG. 12 shows the result of evaluating the displacement with respect to the decay time by the ring-down method. The feature time τ obtained by fitting to this attenuation curve is 321 ms, and as a result, the quality factor Q is estimated to be 420000 or more. Quality factor Q was significantly improved by defect layer etching.
This result means that the defect layer at the bottom of the cantilever induces a large energy loss and reduces the quality factor. It was confirmed that a very high quality factor Q can be obtained by producing a cantilever using only single crystal diamond and removing the defective layer at the bottom of the cantilever.

FIG. 13 is a diagram showing the relationship between the defect layer thickness ratio β in the beam of the cantilever, that is, the ratio of the thickness t _{def of the defect layer to the thickness t cry of the single crystal diamond layer t def} / t _{cry and the quality factor Q.} .. In the figure, along with the experimental results, the curves fitted by the two-layer approximate model based on the experimental results are also plotted.
Here, in this two-layer approximation, the single crystal diamond layer is also defective layer also to have the same Young's modulus, the quality factor Q _cry of single crystal diamond layer was 6,000,000. _{The quality factor Q def} of the crystal layer in the fitting curve of the figure is 1500.

From the results of FIG. 13, the quality factor Q of the cantilever beam is well approximated by a two-layer approximation model consisting of a single crystal diamond layer and a defect layer having different quality factors, and the defect layer becomes thinner and the defect layer thickness ratio β becomes smaller. It can be seen that the quality factor Q becomes larger.
That is, the quality factor Q is remarkably large when the defect layer thickness ratio β is 0.02 or less, further rapidly increases when the defect layer thickness ratio β is 0.01 or less, and is almost the same as the quality factor Q of the single crystal diamond material itself when it is 0.002 or less. It can be seen that the same level of value is reached.

In FIG. 14, cantileveres having different beam lengths are measured, and the quality factor Q in the state before the defect layer etching is performed and the quality factor Q after the defect layer etching is performed for 380 hours with respect to the resonance frequency. It is a figure plotted with.
There is an order of magnitude difference in quality factors between the measurement group with defect layer etching and the measurement group without defect layer etching, and it can be seen that defect layer etching is highly effective in improving quality factor Q.

FIG. 15 shows the resonance frequency characteristics of the cantilever when the measurement temperature is 600 ° C.
The quality factor Q at this time was 20000, and it was confirmed that the cantilever of the single crystal diamond structure of the present invention has a high quality factor Q even in a high temperature environment of 600 ° C.

According to the present invention, a cantilever and a mechanical resonator and a cantilever and a mechanical resonator which bring out excellent heat and mechanical properties such as hardness, Young's modulus, and thermoelastic properties of single crystal diamond and have an extremely excellent quality factor of 500,000 or more. It becomes possible to provide a mechanical resonator.
Further, in MEMS / NEMS using single crystal diamond by a processing method using ion injection, the method of removing the defect layer of the present invention is a method of drawing out the excellent heat and mechanical properties originally possessed by single crystal diamond. Not limited to cantilever, it brings about a great improvement in the performance of MEMS / NEMS, and has the potential to be widely used in industry.

Specific examples thereof include application to various monitors and sensors such as resonance frequency change monitors, AFMs, STMs, temperature sensors, chemical sensors, and magnetic sensors. When the diamond structure of the present invention is applied to these monitors and sensors, it becomes possible to provide monitors and sensors having excellent responsiveness, reliability, temperature range, sensitivity and the like.

Application to monitors and sensors in nuclear reactors and space environments used in radiation and harsh temperature environments is considered to be particularly effective. For example, a sensor using Si as a structure can be applied in an environment up to about 200 ° C due to the temperature characteristics of Si, but when the diamond structure of the present invention is used, high accuracy is achieved even in an environment of 600 ° C. It can be applied with performance, especially under vacuum or under a temperature resistant package, even in an environment of 1000 ° C.

1: Diamond substrate area 2: Ion implantation area 3: Beam (upper part of beam)
4: Beam (resonator bridge part)
5: Diamond substrate area 6: Ion implantation part (support part)
7: Ion implantation part (overhang part)
8: Ion implantation part (beam part)
11: Single crystal diamond layer (base)
11a: Diamond substrate 12: Diamond single crystal structure part 12a: Beam part 12b: Support part 13: Graphite modified layer 13a: Graphite-like carbon damaged layer 13b: Graphite modified layer 14: Defect layer 14a: Defect layer 14b: Defect Layer 15: Diamond epitaxial layer 16: Resist pattern 17: Metal mask 17a: Al film 21: Single crystal diamond substrate 22: Diamond epitaxial layer 23: Substrate 24: Single crystal diamond film 101: Diamond structure (cantilever)

Claims (19)

In a diamond structure in which a diamond beam is formed on a single crystal diamond layer via a support portion.
The beam consists of a surface defect layer and a body layer.
The surface defect layer is made of diamond-like carbon and is made of diamond-like carbon.
The thickness of the surface defect layer is 2% or less with respect to the thickness of the main body layer.
The main body layer is a diamond structure made of single crystal diamond. The diamond structure according to claim 1, wherein the support portion contains graphite. The diamond structure according to claim 1, wherein the support portion is made of graphite. The diamond structure according to claim 1, wherein the support portion includes a diamond. The diamond structure according to any one of claims 1 to 4, wherein the thickness of the surface defect layer is 1% or less with respect to the thickness of the beam. The diamond structure according to any one of claims 1 to 4, wherein the thickness of the surface defect layer is 0.2% or less with respect to the thickness of the beam. The diamond structure according to any one of claims 1 to 6, wherein the beam is a cantilever. A diamond cantilever having the structure of the diamond structure according to any one of claims 1 to 7. A substrate preparation process for preparing a substrate having a single crystal diamond layer formed on at least a part of the surface,
An ion implantation step of forming a graphite-like carbon damaged layer in the single crystal diamond layer by implanting ions from the surface side of the substrate on which the single crystal diamond layer is formed.
The first heat-treated with forming a diamond epitaxial layer on a surface of the single crystal diamond layer, and the first of the graphite-like carbon damage layer Graphite modified layer to the diamond epitaxial layer forming step by heat treatment When,
A high-quality crystallization heat treatment step of applying a second heat treatment to the diamond epitaxial layer to reduce crystal defects of diamond, and
An etching mask forming step of forming an etching mask for forming a beam on the diamond epitaxial layer, and an etching mask forming step.
And dry etching step for processing to form the beam dry etching is performed until at least the Graphite modified layer reaches a depth,
A portion of the Graphite modified layer is removed by wet etching using a solution containing acid, and wet etching process for forming the beam,
A method for manufacturing a diamond structure, comprising: a defect layer etching step of etching at least a part of a defect layer formed on the beam in an oxygen atmosphere, and a method for manufacturing a diamond structure. The method for manufacturing a diamond structure according to claim 9, wherein the substrate is a single crystal diamond substrate. The method for manufacturing a diamond structure according to claim 9, wherein the substrate is a single crystal diamond substrate in which a single crystal diamond layer is epitaxially formed. The method for manufacturing a diamond structure according to claim 9, wherein the substrate is a rigid substrate on which a single crystal diamond film is bonded. The method for producing a diamond structure according to any one of claims 9 to 12, wherein the defect layer etching step is performed under heat treatment conditions of 500 ° C. or higher and 1500 ° C. or lower. The defect layer etching step, the oxygen partial pressure is carried out under the following 10 2 ^Pa or more 10 5 ^Pa environment, producing a diamond structure according to any one of claims 9 13. The method for producing a diamond structure according to any one of claims 9 to 14, wherein the heat treatment in the high-quality crystallization heat treatment step is performed under vacuum at 500 ° C. or higher and 1500 ° C. or lower. The method for producing a diamond structure according to any one of claims 9 to 15, wherein the etching mask is made of metal. The method for producing a diamond structure according to any one of claims 9 to 15, wherein the wet etching is performed with an acid containing sulfuric acid. The method for producing a diamond structure according to any one of claims 9 to 17, wherein cleaning for removing organic substances and / and foreign substances is performed after the defect layer etching step. The method for producing a diamond structure according to claim 18, wherein the cleaning is performed by at least one selected from the group of hydrogen plasma, ozone, and oxygen plasma .

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