JPH08148957A - Piezoelectric thin film wafer and manufacture therefor - Google Patents

Abstract

PURPOSE: To provide a piezoelectric thin film wafer for a surface acoustic wave element with less propagation loss by turning a diamond film formed on a substrate to a mirror finished surface and covering the piezoelectric thin film wafer on it. CONSTITUTION: In a laminated structure body composed of the diamond film B formed on the substrate C and a piezoelectric thin film D formed on the diamond film B, the surface roughness of the diamond film B is less than Rmax 500Å and Ra200Å. Further, this piezoelectric thin film wafer is circular, provided with the diameter of equal to or more than two inches and monotonically warped from an outer periphery towards a center and the warp amount is 2μm<=H<=150μm when it is expressed by ΔH. Further, it is preferrable that the diamond film B be (111) oriented and a C-axis oriented piezoelectric thin film D is easily formed on the (111) oriented diamond film B. Further, it is preferrable that the diamond film B and the piezoelectric thin film D be provided with compression residual stress. The usable piezoelectric thin film D is LiNbO3 , LiTaO3 , AIN or ZnO.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric thin film wafer that can be used in a surface acoustic wave device and a method for manufacturing the same. Diamond has an extremely high sound velocity determined by the ratio of Young's modulus and density. Therefore, the velocity of surface acoustic waves is also very fast,
Surface acoustic wave devices have applications such as filters, phase shifters and convolvers. Although diamond has excellent physical and chemical properties, it cannot produce a large area and inexpensive material. Although bulk diamond can be produced by the synthesis method under ultrahigh pressure and high temperature, only particles or plates having a size of about 1 cm can be produced. Therefore, there is still no thin wafer having a large area like a diamond wafer. It suffices if a thick single crystal ingot such as Si or GaAs can be pulled up by the Bridgman method, but diamond cannot do this.

In order to be applicable in the field of electronics, wafers of at least 2 inches or larger are required. It is highly desirable to be able to manufacture wafers with a diameter of 3 inches or 5 inches. Further, in order to get on the device manufacturing line, the thickness needs to be 3 mm or less. A polycrystalline diamond wafer having a diameter of 2 inches or more and a thickness of 3 mm or less is desired. Furthermore, it would be more convenient if a single crystal diamond wafer could be produced. The use of Si semiconductors and GaAs semiconductors has made it possible to manufacture devices with stable characteristics because of the existence of high-quality single crystal wafers.

[0003]

2. Description of the Related Art Diamond can be formed into a thin film by a vapor phase synthesis method. This is a method of vapor-depositing a diamond thin film by flowing a raw material gas onto a suitable heated substrate. At least hydrogen gas and hydrocarbon gas, or a gas containing boron or a gas containing nitrogen is introduced as a raw material gas, applied to a heated substrate, a thin film is synthesized by a chemical reaction, and the thin film is deposited on the substrate. It is something that goes.

There are several known methods for exciting a gas. There are a hot filament method, a microwave plasma CVD method, a high frequency plasma CVD method, a DC plasma jet CVD method and the like. Depending on the method, it is possible to produce a diamond film having a large area. However, since the synthesis speed is slow, it is difficult to make a very thick film. If you take time, you can make a fairly thick film.

However, it is not known that the entire polycrystalline diamond wafer is mirror-polished. A wafer having a structure in which a piezoelectric thin film is laminated thereon is not known. One of the devices using such diamond is a surface acoustic wave element used for a high frequency filter or the like. For example, JP-A-54-388
As disclosed in Japanese Patent Laid-Open No. 74-74911 and Japanese Patent Laid-Open No. 64-62911, a structure is known in which a diamond thin film or the like has a structure in which an electrode and a piezoelectric body are combined and laminated.
Further, in Japanese Laid-Open Patent Publication No. 5-306195, a method for producing a flat, crack-free, self-supporting diamond film by forming a diamond film on a convex film-forming surface of a substrate and then separating the diamond film from the substrate Is disclosed.

[0006]

The vapor-grown diamond film has unevenness because it has nonuniformity in growth regardless of whether it is a polycrystal or a single crystal. S
Even with the i-wafer, the wafer cut out from the ingot is polished to a mirror surface. Similarly, a diamond wafer must have a mirror-like surface. To obtain a mirror-like polished surface with a Si wafer, attach the wafer to a flat holder, press it against a flat polishing platen, rotate the holder around the shaft, and revolve the polishing platen for free grinding. The lower surface of the wafer is polished by the action of grains or fixed abrasive grains. Since the finished mirror wafer must be flat, it is natural to use a flat holder. S
In the case of an i-wafer, this also successfully polishes 8-inch wafers.

However, diamond is an extremely hard material and can be polished by using fine diamond abrasive grains and applying pressure for a long time. In fact, in the case of a single crystal having a diameter of 1 cm or less or a diamond having a diameter of about several mm, it is polished by the above method,
You can get a mirror surface. The situation is different for diamond wafers with large areas such as diameters of 2 inches or more.

Diamond cannot manufacture polycrystalline or single crystal ingots like Si and GaAs. In the method using ultra-high temperature and high pressure, the size of the pressure vessel is limited, and diamond having a diameter of 2 inches or more can theoretically be manufactured, but it is practically impossible. On the other hand, in the vapor phase synthesis method, it is theoretically possible to synthesize diamond having a considerable size and thickness by prolonging the synthesis time and synthesizing it in a large reaction vessel.

When it is put to practical use industrially, there is always a problem of economical efficiency, and therefore it is not theoretically possible to put it into practical use. As mentioned above, since diamond is an extremely hard material, polishing takes a very long time. The first problem is how to shorten this long polishing time. Next, the growth rate of diamond in the case of synthesizing diamond by the vapor phase synthesis method is extremely slow compared with the growth time of a single crystal such as Si or GaAs. Therefore, the second problem is whether to shorten the synthesis time as much as possible and put the diamond into practical use. Of course, the growth rate of diamond can be increased by the conditions of vapor phase synthesis, but in general, increasing the growth rate of diamond increases the amount of non-diamond carbon and increases the number of defects, resulting in qualitative deterioration. However, there is a limit to the growth rate of diamond.

The inventors have tried to manufacture a diamond wafer having a mirror surface by synthesizing flat diamond on a substrate and polishing it as it is. Attempts were made by variously changing the polishing method, diamond growth conditions, etc., but it was found that the entire surface of the diamond wafer could not be mirror-finished, and the unpolished surface would inevitably remain. This is probably because the synthesis conditions of the large diamond synthesis surface are partially different, diamond is synthesized at high temperature, but thermal strain occurs when it is cooled to room temperature, and the thermal expansion coefficient of the substrate and diamond It is thought to be due to slight waviness due to differences.

If the polishing is carried out for a longer time while ignoring the economical efficiency, the unpolished portion disappears, but this is not practical. It should be noted here that the pressure per unit area decreases as the number of mirror surface portions increases during polishing, so the polishing rate decreases and it takes a longer time to make the entire surface a mirror surface. The diamond wafer must also be thick in order to be able to polish for such a long time. This is because the part that has already become a mirror surface is further polished, and the thickness of diamond becomes thinner.

[0012]

The present application is a laminated structure comprising a diamond film formed on a substrate and a piezoelectric thin film formed thereon, the diamond film having a surface roughness of Rmax 500Å, Ra 200Å or less. Is. Further, the feature of the present application is that the piezoelectric thin film wafer is circular, has a diameter of 2 inches or more, and warps monotonically from the outer circumference toward the center. And when the amount of warp is expressed by ΔH, it is 2
μm ≦ ΔH ≦ 150 μm. Further, in the present application, it is preferable that the diamond film has a (111) orientation, and
11) It is easy to form a C-axis oriented piezoelectric thin film on the oriented diamond film. Further, it is desirable that the diamond film and the piezoelectric thin film have compressive residual stress.

The piezoelectric thin film that can be used in the present application is L
iNbO ₃ , LiTaO ₃ , AlN or ZnO.
Such a piezoelectric thin film wafer can be manufactured by the following method. That is, a step of introducing a raw material gas containing hydrogen and a carbon-containing compound gas into a reaction vessel and growing a diamond film on a substrate by a vapor phase synthesis method, and a step of polishing the diamond film to have a surface roughness Rmax of 500Å, Ra200Å or less. And a step of forming a piezoelectric thin film on the diamond film by a PVD method or a sol-gel method, and the like.

[0014]

The piezoelectric thin film wafer obtained by the present invention is mainly used for surface acoustic wave devices, thermistors, semiconductor devices, etc. It is indispensable to use the above as it is in order to put the present invention into practical use. Therefore, it is desirable that the piezoelectric thin film wafer is a disk having a diameter of 2 inches or more. Since diamond is an extremely hard material, it is a difficult material to process. The cost of processing such as polishing in the piezoelectric thin film wafer is high. FIG. 1 shows a sectional view of the piezoelectric thin film wafer. When the central portion of the disk is convex and the amount of warpage ΔH is defined as a negative value, and the central portion of the disk is concave, ΔH is a positive value. It is necessary to have a monotonic warp from the outer circumference to the center. The unevenness must not be mixed. There should be no inflection point at any cross section through the center of the disc.

Further, the absolute value of the warp is 2 μm to 150 μm.
Between Here, the warp is expressed by the height of the central portion from the plane including the peripheral portion of the piezoelectric thin film wafer. The relationship between the curvature and the warp changes depending on the diameter of the wafer, and even if the warp is the same, the curvature is different. However, since the height of the central portion is the easiest to measure as the amount of warp, this is measured and adopted as a parameter for expressing the warp. The above relationship is 2 μm ≦ |
It can be represented by ΔH | ≦ 150 μm. More preferably, the absolute value is in the range of 3 μm ≦ | ΔH | ≦ 50 μm.

In the present invention, the warpage of the piezoelectric thin film wafer is zero.
I deny that. It seems best that there is no warp. However, when the warp is 0, it often has undulations, the structure of the warp is complicated, and polishing cannot be performed well. An unpolished portion remains or an insufficiently polished region occurs.
When | ΔH | is less than 2 μm, the unevenness due to the waviness of the diamond wafer becomes larger, and the unpolished surface remains and a mirror surface cannot be obtained. Also, | ΔH | is 150
If it exceeds μm, the surface acoustic wave device and the like cannot be manufactured on the existing manufacturing line.

In order to obtain a mirror-like diamond film as in the present application, it is conceivable to make the surface of the substrate into a mirror shape and vapor-phase-synthesize the diamond film thereon. The diamond on the substrate surface side is a copy of the surface state of the substrate, and it should be possible to obtain a diamond wafer having a surface roughness close to a mirror surface. However, a diamond wafer having a mirror surface cannot be obtained by such a method. In the first step of synthesizing diamond from the gas phase, crystal nuclei of diamond are formed on the surface of the substrate. Then, the diamond is preferentially deposited on the crystal nuclei as the center to form island-shaped diamond.

Further growth continues to form a film, and thereafter the film thickness gradually increases. Therefore, in order to obtain a uniform diamond film, it is important to make the crystal nucleus density as high as possible. The crystal nuclei are not generated everywhere but in the active part on the substrate.
Usually, the active points are formed by increasing the surface roughness by means such as scratching the surface of the substrate. Moreover, since carbide is usually formed on the outermost surface of the substrate before the crystal nuclei of diamond are generated and the surface condition is changed, the surface condition of the substrate is not directly transferred to the diamond.

However, the growth surface side of the diamond crystal is inferior in surface roughness to the surface on the substrate side. The crystal growth surface appears on the surface, and there are considerable irregularities. Although it takes a long time to remove the unevenness by polishing, when considering the whole process for manufacturing a diamond wafer, polishing the growth surface side of the diamond crystal is a practical application of the present invention. Can be said to be the best method. It was found that the diamond crystal itself has a compressive stress, a tensile stress, or a state in which almost no stress remains depending on the diamond synthesis conditions.

The diamond film of the present invention can be synthesized by the hot filament CVD method, plasma CVD method and plasma jet CVD method. It is essential to use a carbon-containing gas as the gas used, such as CH ₄ , C ₂ H
Known materials such as ₈ , CO ₂ , and CO can be used. It is common to add H ₂ to these carbon-containing gases. Since an inert gas such as Ar, He, Ne and Kr has the effect of enhancing the stability of plasma, it is particularly effective when the diamond film is synthesized by the plasma CVD method or the plasma jet CVD method. The inert gas turns into plasma and also has an ion bird effect, and is one means for obtaining diamond with high purity. The use of oxygen or an oxygen-containing gas has an effect that oxygen atoms are taken in between the lattices of diamond crystals and a compressive residual stress is easily introduced. In particular, when an inert gas and oxygen are used together and the value of (inert gas) / (inert gas + oxygen gas) is in the range of 0.1 to 0.8 by volume, the effect of adding both gases becomes large. .

A compressive stress is applied in the diamond crystal,
It was found that the most stable self-supporting film can be obtained when the compressive stress is 0.0001 GPa or more and 0.8 GPa or less. When the compressive stress is less than 0.0001 GPa, the sonic velocity of the diamond wafer becomes insufficient, while when the compressive stress exceeds 0.8 GPa, the diamond wafer is more likely to be broken. As a substrate, S
i, GaAs, GaP, etc. can be used. Of these, a Si wafer is particularly desirable.

FIG. 2 is a schematic configuration diagram of a polishing apparatus for obtaining a mirror surface of the present invention. The polishing plate 1 (polishing platen) is a diamond grindstone having a large number of diamond particles fixed on its surface. A resin bond, a metal bond, an electrodeposition grindstone, etc. can be used. This revolves around the main axis.
The holder 3 is an instrument in which a shaft is attached to a flat disc. Sample 2 having a diamond wafer on a substrate,
It is attached to the lower surface of the holder 3 via a cushioning material 11. The holder 3 is tiltable by the shaft 4 and is supported so as to transmit a rotational force. Whereas conventional holders cannot tilt relative to the shaft, the holder of the present invention can tilt relative to the shaft. The cushioning material 11 is an elastic material such as rubber or plastic.

The cushioning material has two roles. The first is to relieve the pressure so that the diamond is not destroyed by the heavy load required to polish it.
It also allows the wafer surface to be slightly tilted with respect to the holder surface. This makes the rocking motion smooth. A drive unit is provided above the shaft 4. There is a bearing and a joint (not shown) here, and rotatably supports the shaft. A pulley is attached to the rotatable part below the joint. Above the joint is a cylinder 5 for applying pressure to the shaft. A large load is required to polish a hard wafer such as diamond.

The cylinder provides this load.
This load gives a concentrated load to the center of the holder. This cylinder is a pneumatic or hydraulically driven cylinder. A laterally extending arm 6 supports the cylinder 5, the shaft 4, and the like.
A motor 7 is further provided on the arm 6. The rotation of the motor is transmitted to the shaft 4 through the motor pulley belt 8 and the shaft pulley. This causes the holder 3 to rotate. The hard wafer also rotates together. The holder revolves around the shaft, and the polishing plate revolves largely around the main axis of rotation (not shown).

In FIG. 3, the holder 3 and the shaft 4 are shown.
The flexible joint 12 is used for the connection. This allows the holder 3 to be tilted by transmitting pressure to the holder and applying a rotational force. Flexible joint 12
Can be, for example, spherical fitting. A circular peripheral groove 13 is formed in the peripheral portion of the holder. The auxiliary shaft 10 slides in this. The holder 3 rotates and the auxiliary shaft does not rotate. However, the auxiliary shaft 10 moves up and down with a small amplitude. When this is lowered, the right side of the holder is lowered. When this goes up, the left side of the holder goes down. Since the polishing surface vibrates to the left and right, the entire diamond surface can be polished. The above is an example of the polishing method when the diamond is convexly warped.

Thus, Rmax of 500 Å or less, R
It is possible to obtain a diamond wafer having a mirror surface of a 200 Å or less. The diamond film formed on the substrate preferably has a (111) orientation. The reason is,
This is because it is possible to easily obtain a C-axis-oriented piezoelectric thin film having the best piezoelectric characteristics among the compressive films. In order to (111) -orientate a diamond film, it is effective to increase the carbon concentration when diamond nuclei are generated and apply a negative bias to the substrate. Any of the hot filament CVD method, plasma CVD method and plasma jet CVD method is effective. Although it can be adopted, the effect is particularly large when plasma is used among the above methods. In order to orient the diamond film in (111) orientation, there is also a method in which the carbon concentration of the supply gas during vapor phase synthesis is relaxed.

Further, the diamond film has a thickness of 0.0001.
It is desirable to have a compressive residual stress of not less than GPa and not more than 0.8 GPa. In the present application, compressive residual stress is indicated using a negative sign. Therefore, positive compressive residual stress means tensile stress. It is extremely important to leave the compressive residual stress in the diamond film in order to make the crystal growth surface side of the diamond film convex on the entire piezoelectric thin film wafer.
The piezoelectric thin film also has a compressive residual stress, and its value is 1 × 10.
It is desirable to have a compressive residual stress of ^-5 GPa to 10 GPa.

The compressive residual stress has the effect of increasing the apparent Young's modulus, increasing the sound velocity, and increasing the piezoelectric characteristics of the piezoelectric thin film, but if it is too high, the probability of destruction of the diamond film and the piezoelectric thin film is high. Becomes higher. The piezoelectric thin film is preferably C-axis oriented. This is because the piezoelectric-thin film has the highest electro-mechanical coupling coefficient when it is oriented along the C-axis. A C-axis oriented piezoelectric film can be further heteroepitaxially grown on the (111) oriented heteroepitaxially grown diamond film.

Various materials are known as the piezoelectric material, but the most excellent material for coating a C-axis oriented piezoelectric thin film on a mirror-finished diamond wafer is LiNb.
It is O ₃ . This material has a high electromechanical conversion coefficient, and a C-axis oriented heteroepitaxial growth can be easily obtained on the (111) plane of a diamond wafer. Besides, LiTaO ₃ , AlN, ZnO or the like can be used. PVD (Physical Vapo) is used as a method for coating a piezoelectric material on a diamond wafer.
ur Deposifiou) method and sol-gel method are excellent. According to this method, the piezoelectric material composed of polyatomic molecules can be deposited on a diamond wafer at low temperature and with good adhesion. A surface acoustic wave element can be provided by further providing an electrode on such a material, or by providing an electrode directly on diamond and depositing the piezoelectric material on the electrode.

[0030]

【Example】

(Example 1) Hot filament CVD on a Si wafer
A diamond thin film was formed by the method. Pressure is 1 to 3
00 Torr, methane / hydrogen ratio is 0.1 vol% to 10
vol%. Since the surface of the diamond film immediately after film formation has very rough surface, it was polished by a mechanical polishing machine to flatten it. The warp of the wafer and the orientation of the diamond film can be controlled by adjusting the gas pressure during deposition, the methane / hydrogen mixture ratio, and the substrate temperature. The result of polishing was greatly different depending on the warp shape of the wafer. With respect to the diamond film after polishing, the film thickness distribution and the surface roughness of the film surface were measured and evaluated by ellipsometry. The film thickness distribution is defined by ((maximum film thickness-minimum film thickness) ÷ average film thickness × 100). Table 1 shows the results. The sound velocity in the diamond film was measured by the ultrasonic pulse method. Moreover, the Young's modulus of the diamond film was calculated from the sound velocity obtained by this measurement. The results are shown in Table 2.

[0031]

[Table 1]

When the warp shape is different, a wafer is prepared,
After polishing each diamond film, the effectiveness of the polished diamond film as a piezoelectric thin film wafer was evaluated. Since the substrate on which the diamond thin film is formed needs to increase the nucleus generation density of diamond in order to uniformly form the film, the surface of the Si wafer is scratched with a diamond paste in advance. The gas used was hydrogen and methane, and the filament material was tungsten. The warp of the diamond-formed Si wafer was controlled by adjusting the substrate temperature during film synthesis. <Hot filament CVD conditions> Pressure: 100 Torr Substrate temperature: 700 to 850 ° C. H ₂ : CH ₄ = 100: 1 Filament temperature: 2100 ° C.

When the substrate temperature is low, the wafer warps so that the diamond surface becomes convex, and when it is high, the wafer becomes concave. The warp amount is represented by a vertical distance from the center of the wafer to a plane including the outer peripheral portion, and in the case of convex warp, the sign of the warp amount is negative. Further, in this case, the stress generated in the diamond film is a compressive stress, and the sign is also negative. In case of concave warping, the opposite is true. The diamond surface of each of the three types of warped wafers having concave, flat, and convex shapes was polished, and the time required until the front surface polishing, the surface roughness of the polished surface, and the diamond film thickness distribution were measured and evaluated.

Samples 1 to 3 each have no warp,
It is a concave and convex warped wafer. Sample 1 has no warp, and Sample 2 has concave warp, but both have longer polishing time and rougher surface accuracy than convex warp. Since the sample 1 has no warp, it is considered that the polishing proceeds easily. But the result was the opposite. Although there is no warp, there is a slight undulation in the wafer surface. This waviness is often present in the form of a mixture of a convex region and a concave region on the surface of one wafer. Therefore, the concave area in the wafer is not polished, and the shape of the polished area is often complicated by reflecting the shape of the convex area, so the friction state during polishing is not stable and the polishing progresses well. do not do.

Sample 2 has a concave warp. This mold does not polish the central part of the wafer due to its shape, and if you try to polish it, you need to polish the surrounding part considerably,
There is a drawback that the polishing time becomes extremely long. Further, the diamond film after polishing has a large film thickness distribution, and the central portion is thick and the peripheral portion is thin. Furthermore, since the polishing time is long, a good polishing surface cannot be obtained because of deterioration of the grindstone, dropping of particles, and the like. On the other hand, Samples 3 and 4 have a large warp and a large warp, respectively. In the case of convex warpage, it is considered that the peripheral portion is not polished, but since the wafer is slightly inclined during polishing, polishing is actually performed.

In Sample 3, the polishing portion spreads uniformly from the center of the wafer toward the periphery, and the progress of polishing is good.
Therefore, the polishing time is short and the surface roughness is fine. Sample 4 has a large amount of convex warpage, and it is difficult to polish the peripheral portion. For this reason, the polishing time becomes long, and the film thickness distribution and surface roughness are worse than those of Sample 3. However, compared to other types of warp (flat or concave), the polishing time and surface roughness were relatively good, even though the absolute value of the warp was large. It turns out to be suitable.

The speed of sound was measured by the ultrasonic pulse method. The film was fixed on the ultrasonic transducer, the pulse echo was observed with an oscilloscope, and the sound velocity was calculated from the time difference between adjacent echoes. The sound velocity of each sample is 8.3 to 15.9 × 10 ³ m
/ Sec is different. The sound velocity increases as the amount of warpage increases in the convex direction of the diamond surface, that is, as the stress in the diamond film increases toward the compression side. The elastic constant was calculated from the sound velocity obtained by the measurement, but it is easier to intuitively understand if the order is reversed. That is, when compressive stress is contained in the film, the distance between carbon atoms is narrowed, and therefore, when compressive stress is applied from the outside, the amount of displacement is relatively small. That is, the elastic constant apparently increases. Sample No. 1 to
The measurement results of No. 4 are shown in Table 2.

[0038]

[Table 2]

As a result, the velocity of the sound wave propagating through the film increases. When forming a surface elastic element by forming a piezoelectric film on a diamond wafer, and under other conditions being equal, the higher the sound velocity of the substrate material (diamond in this case), the higher the frequency of radio waves that can be supported. . This is a very effective element when manufacturing a surface acoustic wave element. That is, when the diamond wafer is used for a surface acoustic wave device, it is found that a diamond film having a compressive stress is very effective.

Example 2 A (111) single crystal Si substrate was set in a reaction chamber of a filament CVD apparatus using tungsten as a filament material, and C was placed in the reaction chamber.
H ₄ and H ₂ gases were introduced at a carbon concentration (CH ₄ / H ₂ × 100 in each gas volume) of 1 to 8%. The pressure in the reaction chamber is 100 to 200 Torr, the filament temperature is 2000 to 2200 ° C., and the substrate temperature is 700.
It was set to ˜900 ° C. Under such conditions, a diamond film (thickness 30 μm) was formed on the single crystal Si substrate. When the diamond film obtained above was evaluated using an X-ray diffractometer, it was found to be polycrystalline, (400),
The plane orientations of (220) and (111) were observed. By simultaneously changing the gas composition ratio and the pressure in the reaction chamber, it was possible to form a polycrystalline diamond film in which the strength ratio of the (111) plane or the (220) plane was changed. In the X-ray diffraction, since the peak intensity is different for each plane, the peak intensity of the (111) plane was set to 100 and the peak intensity of other planes was standardized.

The diamond film thus obtained on the substrate was polished (thickness of the diamond film after polishing: 20).
μm), and a 1 μm thick LiTaO ₃ film was laminated thereon. <LiTaO ₃ thin film forming condition> Pressure: 0.02 Torr Substrate temperature: 580 ° C. Ar: O ₂ = 1: 5 (volume ratio) RF power: 80 W Target: Li: Ta = 3: 2 Sintered body Thickness on this After depositing an Al thin film of 500 Å, a comb-shaped electrode was formed by a photolithography method to manufacture a surface acoustic wave device. Electrode structure (both input and output): 40 pairs (double electrode, normal type) Electrode width: 1.2 μm (center frequency: 1 GHz) Electrode crossing width: 50 × wavelength (wavelength is 8 times the electrode width) Between input and output electrode centers Distance: 50 x wavelength, 80 x wavelength, 11
0 × wavelength The obtained surface acoustic wave device was evaluated based on the operation characteristics using a network analyzer (YHP, 8719A) for the above-mentioned three types of devices having different input-output electrode distances. Was measured and shown in Table 3.

[0042]

[Table 3]

As shown in Table 3, it was found that in the surface acoustic wave device having the LiTaO ₃ / diamond structure, the diamond film having a strong (111) orientation has a reduced propagation loss. ZnO, Li as the material of the piezoelectric film
Similarly, when TaO ₃ was used, the propagation loss was reduced when the diamond film had a strong (111) orientation.

Example 3 A 1 μm-thick LiTaO ₃ thin film was formed by RF sputtering on a diamond film obtained by a vapor phase synthesis method having (311), (110) and (111) orientations. . <LiTaO ₃ thin film forming conditions> Pressure: 0.02 Torr Substrate temperature: 580 ° C. Ar: O ₂ = 1: 10 (volume ratio) RF power: 80 W Target: Li: Ta = 3: 2 Sintered body formed as above When the C-axis orientation was examined by analyzing the LiTaO ₃ film with an X-ray diffractometer, the orientation other than the C-axis was observed in the LiTaO ₃ thin film formed on the diamond film having the (111) plane orientation. Was not done. On the other hand, it was confirmed that the LiTaO ₃ thin film formed on the (311) and (110) oriented diamonds was a mixed film having an orientation other than the C axis. After evaluating the above-mentioned orientation, a comb-shaped electrode is formed on the LiTaO ₃ film using an Al film (thickness: 500 Å),
A surface acoustic wave device was produced and the propagation loss was measured. Table 4
The term “mixed film” means a state in which a-axis alignment, b-axis alignment, and c-axis alignment are mixed, and no alignment in a specific direction is observed.

[0045]

[Table 4]

As shown in Table 4, it has been found that the propagation loss is reduced in the surface acoustic wave device having the LiTaO ₃ / diamond (111) structure.

(Example 4) As in the case of Example 2, a 20 μm thick polycrystalline diamond film was formed on a Si wafer by a filament CVD method under different conditions.
A LiTaO ₃ thin film was formed on it. When the LiTaO ₃ thin film was examined by X-ray diffraction, it was found that the diamond film was (11
As the orientation of 1) is stronger, the LiTaO ₃ thin film is (0
It was confirmed that the orientation of (01) was strong. That is, the (111) plane of diamond and the (001) plane of LiTaO ₃
It was confirmed as shown in Table 5 that it was parallel to the plane (C-axis orientation). An Al thin film was formed on each substrate in the same manner as in Example 2, and then comb electrodes were formed to fabricate a surface acoustic wave device. When the frequency characteristics of the surface acoustic wave device produced in this way were evaluated, it was found that C on (111) diamond was
The surface acoustic wave device having the configuration in which the axially oriented LiTaO ₃ film was arranged could operate at the highest operating frequency.

[0048]

[Table 5]

(Embodiment 5) Diameter of 3 inches, Rmax80Å, Ra20 obtained in the same manner as in Sample 3 of Embodiment 1
A wafer was prepared in which a diamond film having a thickness of 25 μm was coated on the (111) plane of a Si single crystal having a thickness of 0.35 mm. A piezoelectric thin film was coated on the diamond film by a sputtering method. At this time, a negative bias was applied to the substrate. Further, a comb-shaped electrode was formed thereon in the same manner as in Example 2 to fabricate a surface acoustic wave device. However, in the embodiment, A
The ratio was r: O ₂ = 1: 1 (volume ratio). The propagation loss was measured with a network analyzer. Table 6 shows the results of measuring the internal stress of the piezoelectric thin film by X-ray. It can be seen that the product of the present invention provides a piezoelectric thin film wafer with less propagation loss. The negative bias and the residual stress in Table 6 are values related to the piezoelectric thin film.

[0050]

[Table 6]

(Example 6) A (111) single crystal Si substrate was set in a reaction chamber of a CVD apparatus, carbon concentration of CH ₄ and H ₂ was 3 to 20%, and pressure was 10 Torr.
The single crystal substrate is processed for about 5 minutes. (111) Single crystal Si
Carbon reacts with Si on the substrate to form β-SiC,
Furthermore, a buffer layer, which seems to be thin amorphous carbon, was formed on it. Then, -50 ~
By applying a negative bias of −350 V and varying the carbon concentration of CH ₄ and H ₂ within the range of 1 to 5%, the pressure is set to 20.
When the treatment is carried out for about 5 minutes while maintaining the pressure at Torr, diamond grains with uniform crystal orientation grow on the above-mentioned amorphous carbon. Next, the carbon concentration of CH ₄ and H ₂ is set to 0.
Heteroepitaxially grown (111) diamond film could be obtained by synthesizing diamond under a pressure of 40 Torr with fluctuations in the range of 05 to 2%. Surface orientation is RHEER (Reflection High Energy Electron Diffraction)
Confirmed by. After further polishing the growth surface side of the diamond film, a LiTaO ₃ film was laminated in the same manner as in Example 2. It was found that the LiTaO ₃ film was strongly C-axis oriented.

[0052]

The present invention provides a piezoelectric thin film wafer having a small propagation loss by coating the piezoelectric thin film wafer on the diamond film formed on the substrate with a mirror surface. The piezoelectric thin film is provided with a compressive residual stress, whereby the propagation loss of sound waves can be increased, and a high performance piezoelectric thin film wafer for a surface acoustic wave device is provided.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a piezoelectric thin film wafer in which a diamond film and a piezoelectric thin film are formed on a substrate.

FIG. 2 is a schematic perspective view of a polishing apparatus used in the present invention for orbiting a polishing plate to rotate a holder, and tilting the surface of the holder to polish a wafer.

FIG. 3 is a cross-sectional view showing a relationship between a shaft and a holder in a polishing device.

[Explanation of symbols]

 A: Diamond film growth surface B: Diamond film C: Substrate D: Piezoelectric thin film 1: Polishing plate 2: Wafer 3: Holder 4: Shaft 5: Cylinder 6: Arch 7: Motor 8: Belt 9: Cylinder 10: Auxiliary shaft 11 : Buffer material 12: Flexible joint 13: Groove

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihiro Yasato 1-1-1 Kunyokita, Itami City, Hyogo Prefecture Sumitomo Electric Industries, Ltd. Itami Works

Claims (10)

[Claims] 1. A laminated structure comprising a diamond film formed on a substrate and a piezoelectric thin film formed thereon, wherein the diamond film has a surface roughness of Rmax500.
A piezoelectric thin film wafer having a diameter of Å or less and a Ra of 200 Å or less, wherein the diamond film formed on the substrate is a disk having a diameter of 2 inches or more or a rectangular shape having an equivalent area. 2. The piezoelectric thin film wafer according to claim 1, wherein the piezoelectric thin film wafer has a circular shape and is monotonically convexly warped from the outer periphery toward the center. 3. A warp amount ΔH between the outer circumference and the central portion is 2 μm ≦ |
The piezoelectric thin film wafer according to claim 2, wherein ΔH | ≦ 150 μm. 4. The piezoelectric thin film comprises LiNbO ₃ , LiTaO ₃ ,
The piezoelectric thin film wafer according to claim 1, which is AlN or ZnO. 5. The piezoelectric thin film wafer according to claim 1, wherein the diamond film has a (111) orientation. 6. The piezoelectric thin film wafer according to claim 1, wherein the piezoelectric thin film is C-axis oriented. 7. The diamond film is 0.0001 GPa or more,
The piezoelectric thin film wafer according to claim 1, having a compressive residual stress of 0.8 GPa or less. 8. The piezoelectric thin film is 1 × 10 ⁻⁵ GPa to 10 GP.
The piezoelectric thin film wafer according to claim 1, having a compressive residual stress of a. 9. A step of introducing a raw material gas containing at least a carbon-containing compound gas into a reaction vessel and growing a diamond film on a substrate by a vapor phase synthesis method, and the diamond film having a surface roughness of Rmax500Å, Ra200Å or less. A method for manufacturing a piezoelectric thin film wafer, comprising a step of polishing and a step of forming a piezoelectric thin film having a compressive residual stress on the diamond film. 10. A method of manufacturing a piezoelectric thin film wafer, wherein the piezoelectric thin film is formed by applying a negative bias to the substrate and adding an inert gas.