JP3189833B2 - Hard carbon film and substrate for surface acoustic wave device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hard carbon film widely used in general for electronic components and electronic materials (for example, as a heat sink for an inexpensive type laser mount) and a substrate for a surface acoustic wave device having the same.

[0002]

2. Description of the Related Art Conventionally, as a material for a SAW substrate,
LNO (lithium niobate), LTO (lithium tantalate), quartz, sapphire, ZnO and the like are used. In addition, as a material for the heat sink, single crystal diamond, C-BN, AlN, Cu, Al, or the like is used.

[0003]

However, when a SAW element is manufactured using these materials, there are the following problems. For example, diamond with high crystallinity
Unevenness in which the crystal facet (facet) of (111) (100) protruded was easily formed, and it was very difficult to smooth the surface by polishing. In particular, it is very difficult to flatten the surface of the film because diamond has the highest hardness among materials. Therefore, when a piezoelectric layer is formed on diamond to produce a SAW element,
Microscopic irregularities are formed on the surface of the piezoelectric layer. As a result, in a SAW filter having a piezoelectric layer / diamond laminated structure of 1.0 GHz or more, although the operating frequency is at a satisfactory level, the wavelength becomes short at such a frequency, so that the propagation loss increases,
There is a problem that the loss of the filter increases.

At present, it is difficult to obtain a single crystal diamond by the vapor phase synthesis method, and the diamond film obtained by the vapor phase synthesis method must be a polycrystalline film. Therefore, a grain boundary exists in such a diamond film. Since the surface acoustic waves are scattered due to the presence of the grain boundaries, when a diamond film obtained by a vapor phase synthesis method is used for a SAW filter, the propagation loss increases, and the characteristics of the SAW filter are reduced. The tendency to decrease tended to occur.

Further, diamond-like carbon (diamond-like carbon) having a sound speed equivalent to that of diamond
n; diamond-like carbon), it is easy to obtain a flat film, but when forming a piezoelectric layer,
Phenomena such as the carbon portion evaporating in a vacuum are likely to occur. For this reason, it is difficult to form a device using the carbon, and even if a SAW element is manufactured using the carbon, there is a problem that a propagation loss is large.

For heat sink applications, ultrahigh-pressure single-crystal diamond and the like have high thermal conductivity, but are expensive, and the demand for inexpensive (or easy-to-manufacture) materials having appropriate thermal conductivity is increasing. Was.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been made in consideration of the above circumstances. A surface acoustic wave using a hard carbon film which can reduce propagation loss when used in a SAW device and can be manufactured at low cost. It is an object of the present invention to provide an element substrate.

[0008]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a mixed film of graphite-like diamond having specific properties and carbon clusters is extremely effective in achieving the above object. Was.

The hard carbon film (hereinafter referred to as the hard carbon film of the present invention) used for the substrate for a surface acoustic wave device of the present invention is based on the above findings. It is characterized by being composed of a mixed film of clusters (fine graphite) and having a continuous crystal structure in the mixed film.

According to the findings of the present inventors, the hard carbon film of the present invention having the above-mentioned structure is usually composed of graphite-like diamond which occupies most (preferably 90% or more) of the hard carbon film; It is presumed to consist of adjacent diamond grains and carbon clusters that fill the gap between the diamond grains.

In a conventional SAW filter, a surface wave is inevitably scattered at a grain boundary of diamond, thereby causing a propagation loss. On the other hand, in the hard carbon film of the present invention, the diamond continuity is comparable to that of a single crystal because the diamond crystal grains are close to graphite and the space between adjacent diamond grains is filled with carbon clusters. Kept at the level. Therefore, according to the present invention, the propagation loss can be reduced to a level comparable to the case where single crystal diamond is used.

Further, the hard carbon film of the present invention is essentially at the same level as diamond (for example, in terms of physical properties and hardness), and therefore has a sound velocity equivalent to that of high-quality diamond with respect to SAW. . In addition, in the hard carbon film of the present invention, the plane parallel to the base metal has few (111) planes of diamond and the crystal is not perfect diamond.
By polishing using a simple diamond grindstone, a very flat surface having a surface roughness (Ra) of 1 nm or less can be easily obtained.

Therefore, when a SAW filter is manufactured using the hard carbon film of the present invention,
The layer of the piezoelectric body can be easily grown flat.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a hard carbon film and a substrate for a surface acoustic wave device according to the present invention will be described below in detail with reference to the accompanying drawings. In the following description, "%" indicating a quantitative ratio is based on "mol" (that is, molar ratio, mol%) unless otherwise specified.

FIG. 1 is a view showing a SAW element 7 using the surface acoustic wave element substrate of the present embodiment. SAW element 7
Is a substrate 2 made of silicon or the like; a hard carbon film 3 of the present embodiment formed on the substrate 2;
It comprises a known piezoelectric layer 4 formed thereon and an electrode 5 formed on the piezoelectric layer 4. The substrate 2, the hard carbon film 3, and the piezoelectric layer 4 form a substrate 6 for a surface acoustic wave device.

The method for growing the hard carbon film 3 is not particularly limited. For example, various methods such as CVD (chemical vapor deposition), microwave plasma CVD, plasma jet, flame, and hot filament are used. Can be used.

The piezoelectric layer 4 is made of ZnO, LiNbO ₃ , L
It can be formed of a known material such as iTaO ₃ or quartz. The thickness of the piezoelectric layer 4 is set according to the type of the piezoelectric material constituting the layer and the desired characteristics (center frequency, fractional bandwidth, temperature characteristics, etc.) of the SAW element 7.
The method for forming the piezoelectric layer 4 is not particularly limited.
D (chemical vapor deposition) method, microwave plasma CVD
Method, PVD (physical vapor deposition) method, sputtering method,
A known method such as an ion plating method can be used. Note that it is preferable to use a sputtering method (particularly, an RF magnetron sputtering method) in terms of uniformity, mass productivity, and piezoelectric characteristics.

The material (metal, semiconductor, etc.), thickness, surface condition (roughness, etc.) of the substrate 2 is not particularly limited as long as the hard carbon film 3 can be laminated thereon. In order to easily manufacture an electronic device, it is necessary to use Si, SiC, GaAs.
It is preferable to use a semiconductor material such as s and AlN.
Also, metals such as molybdenum and stainless steel can be used. When the substrate 2 is formed of Si, the plane orientation of the Si substrate is (100), (110), or (111).
It is preferred that In particular, the plane orientation is preferably (100) from the viewpoint that a cleavage plane can be easily obtained.

In this embodiment, as shown in FIG. 2, the substrate 1 which does not include the piezoelectric layer and is composed of only the base material 2 and the hard carbon film 3 is referred to as a hard carbon substrate.

FIG. 3 is an enlarged view showing the substrate 2 and the hard carbon film 3, that is, the hard carbon substrate 1. As shown in FIG. 3, in the hard carbon film 3, a carbon cluster (fine graphite) 3b exists between diamond grains 3a close to graphite and the diamond grains 3a. That is, the hard carbon film 3 of the present embodiment is composed of a mixed film of the graphite-like diamond 3a and the carbon cluster 3b, and the crystal structure in the mixed film is continuous.

(Confirmation of Existence of Graphite Diamond) In the hard carbon film 3 of the present embodiment, the existence of the graphite diamond 3a is determined by Raman spectroscopy.
The half width (FWH) of the diamond peak around 33 cm ^-1
M) is 6 cm ^-1 or more.

Generally, the stronger the diamond bond (sp ³ , so-called diamond bond), the smaller the FWHM of the diamond peak near 1333 cm ^-1 observed by Raman spectroscopy, and the FWHM is usually 3 to 4 cm. It is ^-1 . Also, an increase in FWHM means that Raman scattering from sp ³ bonds is reduced, one or two of the bonds are broken, and sp or sp ² bonds are increased. And sp ² and s
Since the bond of p is a bond corresponding to graphite, in the present embodiment, “1333c in Raman spectroscopy”
The full width at half maximum (FWHM) of the diamond peak near m ^-1 is 6c
"m- ¹ or more" is a means for confirming the existence of diamond having graphite properties, that is, the graphite-like diamond 3a. Incidentally, the diamond peak is not necessarily in the 1333 cm ^-1, it is sufficient in the range of 1332cm ^-1 ~1335cm ^-1.

(Confirmation of Existence of Carbon Cluster) In the hard carbon film 3 of the present embodiment, the existence of the carbon cluster 3b is determined as follows: “Raman peak position of graphite is 1
510 cm ^-1 ".

M. Yoshikawa, et al., Physical
According to Review, 46 (11) p7169 (1992), when boron is ion-implanted into glassy carbon, two peaks (1355 cm ^-1 and 1590 cm ^-1 ) of the observed Raman spectrum of glassy carbon are observed.
cm ^-1) is to become one in 1550 cm ^-1.
The reason why the number of peaks is one is that the crystal structure of graphite is reduced.

That is, this study shows that the size of the carbon cluster can be determined by the number of peaks and the position of the peak in the Raman spectrum.

[0026] Reference also documents mentioned above, in this embodiment, the presence of only one peak in the vicinity of 1510 cm ^-1, and the peak around 1510 cm ^-1 FW
Based on the fact that the HM is 170 cm ^-1 or less as a result of the overlap of the two peaks, two to five carbon atoms having sp or sp ² bonds are collected, that is, many carbon clusters 3b are hard. It was presumed that it was present in the carbon film 3. Note that the peak is not necessarily 15
Not need to be in the 10cm ^-1, 1500cm ^-1 ~152
It may be in the range of 0 cm ^-1 .

The above-mentioned "1510 cm ^-1 only that one peak is present in the vicinity, and that FWHM of the peak is 170cm ^-1 or less" is a small graphite structure than reported structure Yoshikawa et al This indicates that a large number is included. Further, the amount of “carbon cluster” can be determined from (Raman intensity of graphite / 60) and Raman spectrum intensity of diamond based on the fact that the Raman spectrum intensity of the graphite component is 60 times the Raman spectrum intensity of diamond. .

The hard carbon film 3 is made of graphite
Balance of abundance of earmonds and carbon clusters
From the point of view, its analysis by Raman spectroscopy
cm ^-1Others for integrated intensity (Id) of nearby peaks
sp^TwoIntensity ratio of integrated intensity (Ic) of peak due to structure
(Ic / Id) is preferably 4 or more.

(Confirmation that the crystal structure is continuous)
“The crystal structure in the mixed film is continuous” means that the FW of the peak existing at 1510 cm ⁻¹
HM is 170 cm ⁻¹ or less ”.

[0030] As described above, FWHM of peaks present in 1510 cm ^-1 in the Raman spectrum (originally, 1355 cm ^-1 and 1590 cm ^-1) two peaks indicating the overlapping degree, that is, the proportion of graphite structure It is an indicator.

The fact that the crystal structure is continuous means that (1) the FWHM of the Raman peak of diamond is 6 cm ^-1 or more, (2) the proportion of the graphite structure contained is small, The fact that diamond grains are broken (ie, graphite) exists between grain boundaries because of the existence of diamond grains between diamond grains. (3) From the Raman spectrum, diamond itself has only diamond bonds. it was found to contain the binding of sp ² to some extent but is supported by.

For example, glass (which is amorphous) transmits light well, because there is no void or single crystal in the glass and the crystal structure is continuous. Such a relationship between light and a crystal structure also applies to a relationship between SAW and a crystal structure.

The fact that the crystal structure is continuous means that S
It is also possible to directly confirm the image by EM (scanning electron microscope) observation. The SEM conditions and observation results at this time are as follows.

Using a SEM of Hitachi S-800, observation is performed under the conditions of electron beam: 5 kV, 10 μA.

FIGS. 18 to 20 show the S of the surface after polishing a diamond CVD film having no carbon cluster.
An EM photograph is shown. In these photographs, the grain boundaries appear white because no carbon clusters exist between adjacent diamond grains. In the case of diamond, the grain boundaries are observed due to charge-up.

FIGS. 21 to 22 show similar SEM photographs of a hard carbon film in which carbon clusters exist between diamond grains (the hard carbon film of the present embodiment). In these photographs, since the carbon clusters exist between the diamond grains and the crystal structures of the carbon clusters and the diamond grains themselves are close, the density of the grain boundaries is not observed.

(Crystalline Diamond Peak) The hard carbon film 3 of the present embodiment shows a peak corresponding to crystalline diamond in X-ray diffraction. An example of such an X-ray diffraction spectrum is shown in the graph of FIG.

This X-ray diffraction is preferably performed under the following conditions (a plane parallel to the substrate, that is, a plane dominant on the surface is examined by the 2θ-θ method).

<Conditions for X-ray Diffraction> X-ray tube: rotating anti-cathode X-ray tube X-ray diffractometer: manufactured by Rigaku Corporation, trade name: RINT-150
0 Target: Cu target Tube voltage: 50 kv Tube current: 32 mA

Under these conditions, 25 by the 2θ-θ method
° to 145 ° and the diamond (11
Check the presence and intensity of peaks corresponding to 1), (220), (311), (400), and (331).

(Presence / absence of diamond peak) For each of the above-mentioned diamond peaks, the intensity of each diamond peak was determined as a relative value with respect to the background (intensity = 10) in the X-ray diffraction spectrum obtained by the above analysis. When expressed, any peak intensity is 1000
If 0 or more, "Diamond peak exists"
Is determined.

In order to check the respective peak intensities, the intensity of the (111) plane where the peak value exists at 43 to 46 ° is calculated by taking the integral section as an angle ± 1 ° at which the peak value exists.
The result obtained by the line diffraction is integrated, and the value obtained by this integration is defined as I (111).

On the other hand, the intensity of the (220) plane having a peak value in the range of 73 to 76 ° is integrated with the result obtained by X-ray diffraction by similarly setting the integration interval to the angle where the peak value exists ± 1 °. The value obtained by this integration is defined as I (220).
In the present embodiment, in view of the balance between the abundances of the graphite-like diamond and the carbon cluster, the ratio of the integrated intensity obtained above, I (111) / I (220)
Is preferably 0.3 or less. Also, I
The value of (111) / I (220) is more preferably in the range of 0.05 to 0.2. In such a range, the ratio of the (111) plane is small, and a flat surface can be easily obtained.

(Raman spectroscopy) Hard carbon film 3 of the present embodiment
Shows that the FWHM of the diamond peak near 1333 cm ^-1 in the Raman spectroscopy is 6 cm ^-1 or more when fitted with a Lorentz curve. The hard carbon film 3 of the present embodiment has a minute carbon cluster peak near 1515 cm ^{-1 in} Raman spectroscopy. Here, "fitting with Lorentz curve" means fitting according to Lorentz theory. This is based on the fact that a Raman spectrum that is scattered by lattice vibration (phonon) due to atoms or molecules in a solid is generally represented by a Lorentz-type equation.

FWHM of diamond peak is 6 cm ^-1
From the above (normally, the FWHM of a single crystal diamond is 3 cm ⁻¹ or less), it is estimated that the diamond of the present embodiment is a diamond close to graphite.

From the viewpoint of reducing the propagation loss when the SAW filter is manufactured, the ratio (Ic) of the integrated intensity (Ic) of the peak of the carbon cluster to the integrated intensity (Id) of the peak of diamond is reduced.
/ Id) is preferably 4 or more. The definition of the integration of the Raman spectrum used in the present embodiment,
This is shown in the graph of FIG.

Originally, in the Raman peak of graphite,
There are peaks at 1580 cm ^-1 and 1355 cm ^-1 .
However, when the crystal becomes very small, that is, when the carbon cluster becomes dominant, the peak becomes 15
It is known to be 10 cm ^-1 . Further, the hard carbon film 3 of the present embodiment has only a peak at 1510 cm ^-1 . This indicates that the carbon clusters contained in the hard carbon film 3 are as small as possible between adjacent diamond grains.

[0048] The peak of the carbon clusters, i.e. FWHM based on the overlap of the peak of 1580 cm ^-1 and 1355 cm ^-1, the result obtained by Lorentz fitting was 170cm ^-1 or less. In the hard carbon film 3 of the present embodiment, the presence of such carbon clusters achieves filling between diamond grains. Based on such a specific structure, the hard carbon film 3 of the present embodiment exhibits a characteristic that propagation loss of a surface wave is small.

In the graph of FIG. 5, that Ic / Id is 4 or more means that the hard carbon film 3 contains carbon clusters to some extent. When the integrated intensity ratio Ic / Id (carbon cluster / diamond) is out of the above range, that is, Ic / Id
In the case of <4, the characteristics of the surface acoustic wave are reduced, and in particular, the propagation loss tends to increase.

The relative intensity of the Raman line calculated from the Raman spectrum of the graphite component is about 60 times the relative intensity of the diamond component. Therefore, when the relative intensity ratio of Raman between the carbon cluster and the diamond is 4 or more, the ratio is 6.6% or more. In consideration of measurement errors, the calculation includes about 5% or more of carbon clusters. Raman spectroscopy is suitably performed under the following conditions.

<Conditions of Raman spectroscopic analysis> Analysis method: Raman spectroscopic scattering method Raman spectroscopic device: manufactured by Zipavon Co., Ltd., trade name: Diroll Light source: argon laser having a wavelength of 457.92 nm Output: 250 mW × 10 times (microscopic Raman spectroscopy) Focus: Adjust to the surface of the hard carbon film.

(Surface Roughness) The surface roughness (surface roughness) of the hard carbon film 3 of this embodiment is preferably 10 nm or less from the viewpoint of disconnection yield.
In the present embodiment, JIS B
Ra specified in -0601 is used. This surface roughness Ra
Can be suitably measured by the following method.

<Measurement Method of Surface Roughness> Using a center line average roughness measuring instrument, a measurement length of 10 μm was sampled, the cross-sectional curve was folded back from the center line, and the area obtained by the roughness curve and the center line was measured. And the value obtained by dividing the measured length by 10 μm is represented by (μm).

(Grain Size) From the viewpoint of reducing the propagation loss of the SAW element 7, the hard carbon film 3 of the present embodiment has a grain size (average crystal grain size) equal to or smaller than the wavelength of the SAW used. Preferably, it is formed. More specifically, when the wavelength of the SAW to be used is λ, the grain size is preferably about 1.0 × λ or less (furthermore, about 4/5 × λ or less). In the present embodiment, the grain size can be suitably measured by the following method.

<Measurement method of grain size> 10 mm ×
A sample of the hard carbon film 3 having a size of 10 mm × 0.3 mm was prepared, annealed at 700 ° C. for 1 hour in the atmosphere, and then the surface of the hard carbon film 3 was observed by SEM (magnification: 5000 times). And measure the grain size.

(Thermal Conductivity) From the viewpoint of heat radiation characteristics after the SAW element is formed, the thermal conductivity of the hard carbon film 3 is 2 W /
It is preferably in the range of not less than cmK and not more than 15 W / cmK. In the present embodiment, the thermal conductivity is, for example,
It can be suitably measured by a known laser flash method.

As described above, in the hard carbon film of the present embodiment and the substrate for a surface acoustic wave device having the same, the diamond crystal grains are close to graphite, and the carbon cluster 3 is located between the adjacent diamond grains 3a.
Since it is filled with b, the continuity of the crystal is maintained at a level comparable to that of the single crystal. Further, since the crystal of the hard carbon film is not perfect diamond, the surface can be easily flattened. Therefore, according to the SAW device including the hard carbon film of the present embodiment, the propagation loss can be reduced to a level comparable to the case where single crystal diamond is used.

Further, since the hard carbon film of the present embodiment is formed of graphite diamond,
It can be manufactured at low cost as compared with the case where a single crystal of diamond is used.

[0059]

The present invention will be described more specifically below with reference to examples.

Example 1 Using a filament CVD (chemical vapor deposition) apparatus 10 shown in FIG. 6, a surface acoustic wave device was manufactured through the steps of FIGS. 7 (a) to 7 (e). The CVD apparatus 10 mainly includes a base support 11 for supporting the base 20, a tungsten filament 12 for heating the base 20, and a bell jar 13 for accommodating the base 11 and the tungsten filament 12. It is configured. The bell jar 13 has a gas introduction pipe 14 for introducing methane gas and hydrogen gas, a cooling water introduction pipe 15 for introducing cooling water for cooling the substrate 20, and a cooling water discharge pipe for discharging the cooling water. 16 and a vacuum pump 17 for evacuating the inside of the bell jar 13 are connected.

First, as shown in FIG. 7A, a 30 μm-thick hard carbon film 21 is formed on the (100) plane of a 350 μm-thick Si base material 20 by such a CVD apparatus 10. Formed to produce a hard carbon substrate. The CVD conditions used at this time are as follows.

The distance between the filament W-Si substrate: 50 mm Pressure: 10 torr (The inside of the bell jar is about 10 to 200 t by a vacuum pump.
The pressure was reduced to orr. CH ₄ : 50 SCCM H ₂ : 1000 SCCM Filament temperature: around 2100 ° C. (adjust the filament power supply to obtain this temperature) Substrate temperature: around 750 ° C. (adjust the cooling water temperature to obtain this temperature)

When the surface of the hard carbon film 21 formed as described above was observed by SEM (scanning electron microscope, magnification: 3000 times), the particle size was several tens μm. Further, when the hard carbon film 21 was subjected to X-ray diffraction (Cu tube, θ-2θ scanning), it was found that 43.8 ° diamond (11
1), 75.8 ° diamond (220), 90.8 °
Diamond (311), 119.7 ° diamond (400), and 140.8 ° diamond (33
Each peak of 1) was observed.

Eight hard carbon substrates having a structure of hard carbon film / Si base were prepared under the above-mentioned conditions, and the peak value was 43
The intensity of the (111) plane existing at ４６46 ° was integrated with the result obtained by X-ray diffraction with the integration interval being the angle at which the peak value was ± 1 °, and the integrated intensity I (111) was obtained. On the other hand,
The intensity of the (220) plane where the peak value exists at 73 to 76 ° is defined as X with the integration section as an angle ± 1 ° at which the peak value exists.
The result obtained by the line diffraction is similarly integrated, and the integrated intensity I (2
20) was obtained. Then, the ratio of each integrated intensity, I
When the values of (111) / I (220) were determined, they were all 0.3 or less as shown in the graph of FIG.

[Table 1]

In the Raman spectrum using an Ar laser, a relatively low peak (intensity: Id) for diamond was observed at 1333 cm ⁻¹ , but 1530 c
There was a broad peak at m ^{-1 to} 1650 cm ^-1 (Ic), and the integrated intensity ratio was (Ic / Id) = 5.

Next, as shown in FIG. 7B, the surface of the hard carbon film 21 formed as described above is coated with a grindstone made of natural diamond abrasive grains (abrasive grain size # 200 (5 to 20 μm).
m)) to finish the surface to 20 nm (Ra).

Next, as shown in FIG. 7C, a piezoelectric layer 22 made of ZnO was formed on the hard carbon film 21 to produce a substrate for a surface acoustic wave device. Specifically, a 1050 nm-thick piezoelectric layer 22 was formed on Samples A and B (hard carbon film / Si substrate) by RF sputtering under the following conditions.

Substrate: Diamond / Si wafer Sample A Sample B Target: Sintered body of ZnO RF power: 500 W (frequency 13.56 MHz) Reaction gas: Type Ar + Oxygen Ar: 0 ₂ = 1: 1: Flow rate 50 sccm Gas pressure: 20.0 Pa Film forming temperature (substrate temperature): 150 ° C. Film forming rate: 5 nm / min Film thickness: 1050 nm (1.05 μm)

Next, as shown in FIG. 7D, on the piezoelectric layer 22 made of ZnO, a thickness 80
An Al film 23 of nm was formed by DC sputtering. The conditions at this time are as follows.

DC sputtering power: 1.0 kW Reactive gas: argon gas flow rate 50 sccm Gas pressure: 1.0 Pa (7.6 mTorr) Film forming temperature (substrate temperature): room temperature Aluminum film thickness: 80 nm

Further, as shown in FIG. 7E, a part of the Al film 23 is removed by photolithography to form a comb-shaped electrode 24 having the following parameters, and a surface acoustic wave (SAW) element 25 is completed. I let it.

Electrode width: 0.8 μm (center frequency: 1.75 GHz) Number of electrodes: 40 pairs of double electrodes (regular type) Electrode cross width: 50 × wavelength (the wavelength is eight times the electrode width, λ = 6.4 μm) Electrode center distance: 50 x wavelength

FIG. 9 shows a pattern of the comb electrode 24.
As shown in FIG. 9, two electrode strips 31 are arranged, four strips have one wavelength, and the blank portion 32 has the same width as the electrode strip 31. Double becomes the wavelength. Further, electrode pairs are provided on the left and right sides of the element. That is, the number of electrodes on one side is 40 pairs.

Further, the propagation loss and the conversion loss of the surface acoustic wave device 25 manufactured in this embodiment were measured using a vector network analyzer (HP8753c). A high frequency power of 1 GHz to 2 GHz was applied between one electrode, and the power at that electrode and the power appearing between the electrodes on the opposite side were measured to determine the S parameter. S11
Represents the reflected power coming out of the electrode 1 when power is input to the electrode 1. S22 indicates the reflected power that is output to the same electrode 2 when power is input to the electrode 2. S21 and S12 are
When the high frequency power is applied to the electrode 2 or the electrode 1, the power output from the electrode 1 or the electrode 2 on the opposite side is shown. That is, it indicates the transmitted power.

FIG. 10 shows S12. The horizontal axis is frequency. The vertical axis indicates the power of the signal that has reached the electrode 2 and is expressed in dB. As shown in FIG.
At GHz, the transmitted power shows a peak (-8.2 dB). The wavelength λ is determined by the shape of the electrode as described above, and the velocity V of the surface acoustic wave is determined by diamond, so that the surface acoustic wave element 25
The frequency f = V / λ that can pass through is determined from the beginning. This frequency is 1.78 GHz. At this frequency, the transmitted power is -8.2 dB. However, this value includes all losses such as (1) resistance loss at the electrode, (2) loss due to signal spreading in both directions, and (3) conversion loss. The propagation loss is the total loss
2 dB minus these losses.

The resistance loss is such that Al has a thickness of 80 nm and a width of 0.1 mm.
It can be calculated from 8 μm, and the value is 1.0 dB. The bidirectional loss that occurs in both directions and halves the power is 6
dB. FIG. 11 shows S11, and FIG. 12 shows S22. The conversion loss can be seen from the loss (0.3 dB) of the flat portion other than 1.78 GHz in S11 and S22. Since this loss occurs at both electrodes, the conversion loss is 0.6 dB. Since the total loss at these electrodes is 7.6 dB, subtracting this from 8.2 dB shows that the propagation loss is actually only 0.6 dB.

This is a loss during propagation between the electrodes on both sides, and the distance between the centers of the electrodes on both sides is 50 wavelengths. The loss per wavelength is 0.6 dB divided by 50,
It becomes 0.012 dB. This is an extremely small value for a high frequency of 1.8 GHz. It can be clearly understood that the surface acoustic wave device 25 using the surface acoustic wave device substrate of the present embodiment is excellent.

One of the hard carbon films obtained in Example 1 was subjected to Raman spectroscopy using an argon laser having an oscillation wavelength of 457.92 nm which is different from the usual wavelength of 514.5 nm. An example of the results, as shown in FIG. 13, the vicinity of the diamond peak 1333 cm ^-1 15
Only a peak near 15 cm ^-1 was observed, and the diamond Raman spectral peak (1333 cm ^-1)
FWH of the peak
M was 7 cm ^-1 . That is, this hard carbon film
Graphite-like diamond and carbon clusters were mixed.

Example 2 In order to change the ratio including the carbon clusters and the diamond film quality, the diamond synthesis conditions, particularly the ratio of the methane concentration to hydrogen, was set to 0.5 to 0.5 by the filament CVD method.
A hard carbon substrate composed of five Si substrates and a hard carbon film was produced in the same manner as in Example 1 except that the value was changed to 3%. The diamond film thickness of each of the obtained substrates was 20 μm or more, and it was found that the substrates could sufficiently produce a SAW element.

The detailed diamond synthesis conditions used here are shown in Table 2 below.

[Table 2]

Hard carbon substrates (five types) composed of a Si substrate and a hard carbon film were measured by Raman spectroscopy, and the Raman spectral peak (1333 cm ⁻¹ ) of diamond was fitted with a Lorentz curve to determine the FWHM of the peak. .

Further, SAW devices were manufactured in the same manner as in Example 1, and propagation loss was measured for these five types of SAW devices to determine the relationship between FWHM and propagation loss. The relationship between the obtained diamond FWHM and propagation loss is shown in the graph of FIG. As can be seen from this figure, FWH
When M is 6 cm ^-1 or more, a favorable result that the propagation loss is reduced is obtained.

Further, the prepared hard carbon substrates (five types)
Was measured by Raman spectroscopy, the diamond Raman spectroscopy peak (1333 cm ^-1) fitting at Lorenz curve to determine the exact position of the diamond peaks (cm ^-1). FIG. 15 is a graph showing the relationship between the obtained diamond peak position and propagation loss.

The prepared hard carbon substrates (five types) were measured by Raman spectroscopy, and the Raman spectral peak (around 1515 cm ^-1 ) of the carbon cluster was fitted with a Lorentz curve to determine the FWHM of the peak. further,
With respect to these five types of substrates, the propagation loss was measured in the same manner as in Example 1, and the relationship between the FWHM of the carbon cluster and the propagation loss was determined. The obtained graphite FWH
FIG. 16 shows the relationship between M and the propagation loss.

Using a hard carbon substrate (5 types), 151
5cm ^-1 vicinity of the integrated intensity of the center position value ± 35 cm ^-1 peak (Ic), obtains the integrated intensity of the center position value ± 5cm ^-1 peak around 1333 cm ^-1 (Id), carbon clusters as described above Intensity ratio of Raman light between diamond and diamond (I
c / Id) was calculated. Furthermore, SAW devices were manufactured for these five types of substrates, and propagation loss was measured in the same manner as in Example 1, to determine the relationship between Ic / Id and the propagation loss.

FIG. 17 is a graph showing the relationship between the obtained Ic / Id and the propagation loss. As can be seen from this graph, when the intensity ratio Ic / Id is 4 or more, a favorable result that the propagation loss is reduced is obtained.

[0087]

As described above, the surface elasticity of the present invention is
In the wave element substrate, the diamond continuity is maintained at a level comparable to that of a single crystal because the diamond grains are close to graphite and the space between adjacent diamond grains is filled with carbon clusters. . Further, since the crystal of the hard carbon film is not perfect diamond, the surface can be easily flattened. For this reason,
SAW manufactured using the surface acoustic wave device substrate of the present invention
According to the element, the propagation loss can be reduced to a level comparable to the case where single crystal diamond is used.

Further, since the hard carbon film of the present invention is formed of graphite-like diamond, it can be manufactured at a lower cost as compared with the case where a single crystal of diamond is used.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a SAW element manufactured using a surface acoustic wave element substrate of the present invention.

FIG. 2 is a view showing a hard carbon substrate composed of a base material and a hard carbon film.

FIG. 3 is an enlarged view of a substrate and a hard carbon film shown in FIG.

FIG. 4 is a graph showing an example of a spectrum obtained by X-ray diffraction of the hard carbon film of the present invention.

FIG. 5 is a graph showing an example of a spectrum obtained by Raman analysis of the hard carbon film of the present invention.

FIG. 6 is a schematic sectional view showing a filament CVD apparatus used in Example 1.

FIG. 7 is a manufacturing process diagram of the SAW element manufactured in Example 1.

FIG. 8 is a graph showing the orientation, I (111) / I (220), of the hard carbon film of the present invention obtained in Example 1.

FIG. 9 is a schematic diagram showing a pattern of an electrode manufactured in Example 1.

FIG. 10 is a graph showing S12.

FIG. 11 is a graph showing S11.

FIG. 12 is a graph showing S22.

FIG. 13 is a graph showing an example of a Raman spectrum obtained in Example 1.

FIG. 14 is a graph showing an example of a relationship between FWHM of a diamond peak and propagation loss.

FIG. 15 is a graph showing an example of a relationship between a peak position of a diamond peak and a propagation loss.

FIG. 16 shows the FWHM of the carbon cluster peak,
9 is a graph illustrating an example of a relationship with a propagation loss.

FIG. 17 is a graph showing an example of a relationship between a ratio Ic / Id of integrated intensity and a propagation loss.

FIG. 18: Diamond CV without carbon cluster
It is a SEM photograph which shows an example of the surface after polishing of D film (magnification 1K = 1000 times).

FIG. 19 is an SEM photograph showing the same surface as in FIG. 18 (magnification 3K = 3000 times).

FIG. 20 is a SEM photograph showing the same surface as in FIG. 18 (magnification: 10K = 10000 times).

FIG. 21 is an SEM photograph showing an example of a hard film having a carbon cluster at a grain boundary (hard film of the present invention) (magnification: 3).
K = 3000 times).

FIG. 22 is an SEM photograph showing the same surface as in FIG. 21 (magnification: 10K = 10000 times).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Hard carbon substrate, 2 ... Base material, 3 ... Hard carbon film, 3a ...
Diamond particles, 3b: carbon cluster, 4: piezoelectric layer, 5: electrode, 6: substrate for surface acoustic wave device, 7: SA
W element, 10 ... filament CVD apparatus.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yuichiro Seki 1-1-1, Koyokita-Kita, Itami-shi, Hyogo Sumitomo Electric Industries, Ltd. Itami Works (72) Inventor Hideaki Nakahata Kitaichi-Kunyo, Itami-shi, Hyogo 1-1 1-1 Sumitomo Electric Industries, Ltd. Itami Works (72) Inventor Shinichi Shikata 1-1-1, Koyokita-Kita, Itami-shi, Hyogo Prefecture Itami Works Sumitomo Electric Industries, Ltd. (56) References 5-320911 (JP, A) JP-A-6-316492 (JP, A) JP-A-9-71498 (JP, A) JP-A-7-45748 (JP, A) JP-A-6-232677 (JP, A) A) JP-A-5-90874 (JP, A) Ceramics 27 [3] (1992) pp. 219-225 Proc. spie-Int. SoC. Opt. Eng. (Diamond opt. V) 1759 (1992) p70-80 Diamond and Related Materials 8 (1999) p. 1913-1918 Surface technology 42 [12] (1991) p. 1185 -1188 (58) Fields investigated (Int. Cl. ⁷ , DB name) H03H 9/25 C01B 31/02 101 C23C 16/27 C30B 29/04 CA (STN) ELSEVIER

Claims (8)

(57) [Claims] 1. A mixed film of graphite-like diamond and carbon cluster, wherein the mixed film has a continuous crystal structure, and the graphite-like diamond has a wavelength of 457.92.
Pi in the Raman spectroscopic analysis using nm argon laser beam in the range of 1332~1335cm ^-1 - has a click and is the half width of the peak is 6 cm ^-1 or more, the carbon cluster, wavelength 457. 92nm
140 in Raman spectroscopy using Lugon laser light
1500 to 1520 cm within the range of 0 to 1700 cm ^-1
A single peak in the range of ^-1 and a half-value width of the peak is 170 cm ^-1 or less, and a peak obtained by Raman spectroscopy of the graphite-like diamond (position P1 where the peak value exists: 1332-133)
5 cm ^-1 ), the integrated intensity integrated in the section of P1 ± 5 cm ^-1 is defined as Id, and the peak of the carbon cluster by Raman spectroscopy (the position P2 where the peak value is present P2 = 150
A hard carbon film having a value of Ic / Id of 4 or more is used , where Ic is the integrated intensity obtained by integrating Pc in a range of P2 ± 35 cm ^-1 for 0 to 1520 cm ^-1 ) .
Substrate for a surface acoustic wave device . 2. The integrated intensity obtained by integrating the peak of the (111) plane in the X-ray diffraction of the graphite-like diamond (the position where the peak value exists, P3 = 43 to 46 °) in the section of P3 ± 1 ° is I (111). ), The peak of the (220) plane in the X-ray diffraction of the graphite-like diamond (the position P4 where the peak value exists).
73-76 °), the value of I (111) / I (220) is 0.3 or less, where I (220) is the integrated intensity obtained by integrating in the section of P4 ± 1 °. The substrate for a surface acoustic wave device according to claim 1 . 3. The value of I (111) / I (220) is:
Claims characterized by being in the range of 0.05 to 0.2
3. The substrate for a surface acoustic wave device according to 2 . 4. The table according to claim 1, wherein the average grain size of the graphite-like diamond is at least 1.0 times the wavelength λ used in the surface acoustic wave filter.
Substrate for surface acoustic wave device . 5. The thermal conductivity of the hard carbon film is 2 W / cm.
2. The surface according to claim 1, which is not less than K and not more than 15 W / cmK.
Substrate for elastic wave device . 6. A substrate, said hard carbon film disposed on the substrate, the surface of claim 1 in which a piezoelectric layer disposed on the rigid carbon film, comprising the Substrate for elastic wave device. 7. The piezoelectric layer is made of ZnO, LiNbO ₃ ,
7. The surface acoustic wave device substrate according to claim 6 , wherein the substrate is made of LiTaO ₃ or KNbO ₃ . 8. The substrate for a surface acoustic wave device according to claim 6 , wherein said substrate is made of Si.