Vibration plate composite body

Abstract

(Task) Provision of a composite body of a vibratory plate consisting of a high-strength ceramic and a support substrate, wherein the composite body has the structure to maintain the strength of the vibratory plate and to prevent peeling and cracking of the vibratory plate. (Solution) A vibratory plate composite body 5 comprises a silicon support substrate 3, a vibratory plate 1A made of a high-strength ceramic with a thickness of 100 µm or less, and a bonding layer 2 between the support substrate 3 and the vibratory plate 1A, which contacts a bonding surface 1a of the vibratory plate 1A and is made of α-Si. The arithmetic mean roughness Ra of the bonding surface 1a of the vibratory plate 1A is 0.01 nm or more and 10.0 nm or less, and the pit density of the bonding surface 1a of the vibratory plate 1A is 10 counts or more per 100 µm. 2 .

Description

Technical field

[0001] The present invention relates to a composite body that can be used for a MEMS mirror (Micro Electro Mechanical System) or the like and is produced by bonding a vibration plate made of a high-strength ceramic to a support substrate. Technical background

[0002] A head-up display (HUD) is a system for displaying essential information that overlaps within the driver's field of vision while maintaining forward-facing focus. Because the information can be visualized while driving, rather than viewing it on a traditional dashboard or instrument panel, it effectively prevents driver distraction. Furthermore, the reduced eye movement can lessen driver fatigue and improve safety.

[0003] The principle of the HUD is described. An image from a fluorescent tube, a cathode ray tube, or a liquid crystal display is projected onto the windshield or a transparent screen (combinator) of the vehicle. Due to the different optical structures, the HUD incorporates the following two systems. (1) Direct projection system in which the image is projected directly onto the windscreen or the like as a screen. (2) Virtual imaging system for imaging the image on the driver's retina by means of the windscreen or the like as a reflective mirror.

[0004] The main difference between these systems is the perceived distance when the driver views the image. With the direct projection system, the image is projected onto the screen (combinator) as with a conventional projector. With the virtual imaging system, the image is projected onto a screen several meters away, within the driver's line of sight. Both systems significantly reduce the shift in the line of sight between the driver's forward field of vision and the display panel or console compared to when the HUD is not in use. However, with the virtual imaging system, the shift in focus during normal driving is minimal, allowing the driver to concentrate better on driving and experience less fatigue. The development of a new scanning laser beam imaging system has been promoted in conjunction with the virtual imaging system.

[0005] According to the laser scanning technology, the laser beams of the three RGB colors are combined by an optical device called a combiner to create a single beam, which is reflected by a micromirror to perform two-dimensional scanning and imaging. Although similar to electron beam scanning in a cathode ray tube, instead of exciting a phosphor, the pulse width and power of the respective laser beams are controlled at positions corresponding to the respective pixels on the horizontal scan lines to change the color and brightness, thus achieving high-speed pointillism of the pixels. The achievable resolution is determined by the oscillation frequency of the mirror and the modulation frequency of the laser.

[0006] The most important advantages of the system include the following. (1) Since the number of parts is small, miniaturization, cost reduction and improvement in reliability can be achieved. (2) Since the laser can be illuminated with the brightness required for each pixel, low power consumption can be achieved. (3) Since collimated laser light (parallel light) is used, adjusting the focus is not necessary.

[0007] The micromirror is a key component of the laser-scan display and is manufactured by processing silicon using MEMS (Micro Electro Mechanical System) technology and by vapor deposition of a metal. The mirror can be driven by an electrostatic system (driven by electrostatic attraction), an electromagnetic system (driven by electromagnetic force), or a piezoelectric system (driven by a piezoelectric device). Advantages of the piezoelectric system include high-speed drive, lower power consumption, and high drive force; disadvantages include the difficulty of film formation in the piezoelectric device. For example, a MEMS mirror using a sol substrate is proposed (Patent Document 1). (Known technical documents) (Patent documents) (Patent document 1) Japanese patent publication no. 2012-037578A (Patent document 2) Japanese patent publication no. 2014-086400A SUMMARY OF THE INVENTION (Problems to be solved by the invention)

[0008] For the HUD, an increase in display size and viewing angle is currently required, and the viewing angle should also be increased from the conventional 7 to 8 degrees to a maximum of 20 degrees. To achieve this increase in display size and viewing angle, it is necessary to improve the frequency, amplitude, and reliability of the piezoelectric element in the MEMS mirror. In particular, an increase in the width and speed of the scan is required. However, such requirements cannot be met with existing piezoelectric elements on a silicon substrate.

[0009] An attempt was made to use a high-strength ceramic plate as a vibrating plate beneath a piezoelectric layer. However, to use the high-strength ceramic plate as such, it is necessary to reduce its thickness to 100 µm or less, thereby increasing the vibration frequency. If the thickness of the high-strength ceramic plate is 100 µm or less, however, the mechanical strength is insufficient. Therefore, efforts are being made to polish the high-strength ceramic plate to a thickness of 100 µm or less after bonding it to a support substrate to create a composite body.

[0010] However, during actual manufacturing, it was found that the high-strength ceramic is difficult to process and the stress during processing (shear stress) is high, leading to problems such as peeling, cracking, and the like. Furthermore, attempts were made to introduce a bonding layer between the vibratory plate and the substrate to improve the adhesion between the two, and to roughen the surface of the vibratory plate to enhance the bonding force between the plate and the bonding layer. However, roughening the surface of the vibratory plate is expected to reduce its flexural strength. Therefore, preventing peeling and cracking in the composite body of the vibratory plate, which consists of the high-strength ceramic and the substrate, is difficult.

[0011] An object of the present invention is to provide a composite body of a vibratory plate, consisting of a high-strength ceramic and having a thickness of 100 µm or less, and a support substrate, wherein the composite body has the structure to maintain the strength of the vibratory plate and to prevent peeling and cracking of the vibratory plate. (Solution to the problem)

[0012] The present invention provides a vibration plate composite body comprising: a silicon-based support substrate; a vibrating plate comprising a high-strength ceramic and having a thickness of 100 µm or less; and a bonding layer between the support substrate and the vibrating plate, which touches a bonding surface of the vibrating plate and comprises α-Si, wherein the bonding surface of the vibrating plate has an arithmetic mean roughness Ra of 0.01 nm or more and 10.0 nm or less, and where the bonding surface of the vibrating plate has a pit density of 10 counts or more per 100 µm 2 exhibits.

[0013] Furthermore, the present invention provides a method for manufacturing a vibrating plate composite body, wherein the method comprises the steps of: Providing a bonding layer on a surface of a high-strength ceramic plate comprising a high-strength ceramic, wherein the bonding layer comprises α-Si; subsequent bonding of a bonding surface of the bonding layer to a bonding surface of a silicon-comprising support substrate; and subsequent machining of the high-strength ceramic plate to obtain a vibratory plate with a thickness of 100 µm or less, wherein the surface of the high-strength ceramic plate has an arithmetic mean roughness Ra of 0.01 nm or more and 10.0 nm or less, and the surface of the high-strength ceramic plate has a pit density of 10 counts or more per 100 µm 2 exhibits. (Effects of the invention)

[0014] In the case where a bulk-type high-strength ceramic plate is bonded directly to a silicon substrate, the plate may not withstand the polishing process required to reduce its thickness to 100 µm or less, leading to peeling or cracking. Therefore, the inventors have attempted to apply an α-Si bonding layer to the bulk-type high-strength ceramic plate and bond this layer to the silicon substrate. The α-Si bonding layer serves to reduce the cost of the etching process, for example, when creating a hollow structure in the vibratory plate. Since the bond strength between the α-Si bonding layer and the silicon substrate is high, the high-strength ceramic plate should withstand the polishing process to a thickness of 100 µm or less.

[0015] However, polishing is subject to the assumption that fractures or cracks can occur at the interface between the high-strength ceramic plate and the bonding layer. This means that since flexural strength is required for the high-strength ceramic plate, its surface must be flat. However, if the surface of the high-strength ceramic plate is flat, the likelihood of peeling or cracking at the flat interface between the high-strength ceramic plate and the bonding layer is higher, as the adhesion of the surface to the surface of the bonding layer (amorphous silicon) is impaired.

[0016] In light of the above, the inventors have attempted to improve the flatness of the surface (bonding surface, on which the bonding layer is to be applied) of the high-strength ceramic plate, finding that peeling or cracking at the interface of the bonding layer during polishing is suppressed, depending on the case, even when the bonding surface is flat.

[0017] The inventors further investigated the vibratory plate composite body, which exhibits properties exceeding expectations. As a result, even in cases where the arithmetic mean roughness (Ra) of the flat bonding surface of the high-strength ceramic plate is extremely low, it was found that pits remain on the bonding surface due to fine cavities, depending on the physical properties of the high-strength ceramic plate, and that peeling is suppressed by the effects of these surface pits. The present invention was thus made.

[0018] This means that if the arithmetic mean roughness Ra of the bonding surface of the vibrating plate exceeds 10.0 nm, the flexural strength of the vibrating plate during vibration is low, so it cannot withstand high-amplitude, high-frequency vibration. Ra is therefore set to 10.0 nm or less to obtain a very flat surface. Even in this case, it has been proven that cracking or peeling of the vibrating plate during the polishing process can be prevented by reducing the pit density of the bonding surface of the vibrating plate to 10 or more per 100 µm. 2 is being discontinued. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1(a) shows the condition in which a bonding layer 2 is provided on a bonding surface 1a of a high-strength ceramic plate 1, Fig. Figure 1(b) shows the state in which a surface 2b of the bonding layer 2 is activated by a neutralized atomic beam, and Fig.Figure 1(c) shows the state in which a bonding surface 3a of a support substrate 3 is activated by a neutralized atom beam. Fig. Figure 2(a) shows a composite body 4 made of the high-strength ceramic plate 1 and the support substrate 3 and Fig. Figure 2(b) shows a composite body 5 consisting of a vibrating plate 1A and the support substrate 3. Fig. Figure 3 is an image measured with an AFM and shows the condition of the surface pits on a bonding surface of the high-strength ceramic plate. FORMS OF EXECUTION OF THE INVENTION

[0019] The present invention is described in more detail below with reference to the drawings.

[0020] As in Fig.As shown in Figure 1(a), a high-strength ceramic plate 1 is produced. The arithmetic mean roughness Ra of a surface 1a of the high-strength ceramic plate is 0.01 nm or more and 10.0 nm or less, and the pit density of the surface of the high-strength ceramic plate is 10 counts or more per 100 µm. 2 . 1b represents a back surface of the high-strength ceramic plate 1.

[0021] A bonding layer 2 made of α-Si is then applied to the surface 1a of the high-strength ceramic plate 1. Then, as in Fig. As shown in Figure 1(b), a neutralized atom beam is directed onto a bonding surface 2a of the bonding layer 2 for activation (arrows A). Furthermore, a neutralized atom beam is directed onto a bonding surface 3a of the support substrate 3 (arrows B) for activation.

[0022] Then, as in Fig.2(a) shows the activated bonding surface 2b of the bonding layer 2 and the activated bonding surface 3a of the support substrate 3 being contacted and directly bonded together to obtain a composite body 4. The back surface 1b of the high-strength ceramic plate 1 of the composite body 4 is then machined to reduce the thickness of the high-strength ceramic plate to form a vibratory plate 1A with a thickness of 100 µm or less, as shown in Fig. 2(b) is shown to obtain a vibratory plate composite body 5. 1c represents a machined surface.

[0023] Although the thickness of the silicon-based support substrate is not particularly limited, it can preferably be 200 µm or greater, and more preferably 400 µm or greater, to maintain strength during processing. Furthermore, the arithmetic mean roughness Ra of the bonding surface of the support substrate can preferably be 1 nm or less, and more preferably 0.3 nm or less, to facilitate direct bonding.

[0024] High-strength ceramics are defined as ceramic materials with a Young's modulus of 200 GPa or greater and a 3-point flexural strength of 300 GPa or greater.

[0025] The high-strength ceramic may preferably be sialon, cordierite, mullite, translucent aluminum oxide, aluminum nitride, silicon nitride or silicon carbide.

[0026] Furthermore, the thickness of the high-strength ceramic plate can preferably be 100 µm or greater, and more preferably 200 µm or greater, to ensure manageability during processes such as cleaning or bonding the substrate. Although the upper limit of the high-strength ceramic plate is not particularly restricted, it can preferably be 300 µm or less to reduce the processing time.

[0027] According to the present invention, the arithmetic mean roughness Ra of the surface (surface on which the bonding layer is provided) of the vibrating plate is 0.01 nm or more and 10.0 nm or less, and the pit density on the surface of the vibrating plate is 10 counts or more per 100 µm. 2. However, since the bonding layer is formed on the vibrating plate of the vibrating plate composite body, Ra and the pit density of the surface of the vibrating plate must be the same as Ra and the pit density of the surface of the high-strength ceramic plate before processing.

[0028] The arithmetic mean roughness Ra of each surface of the high-strength ceramic plate and the vibratory plate is measured as follows. First, the surface is measured with an atomic force microscope (AFM) in a field of view of 10 µm × 10 µm, and Ra is calculated according to JIS B 0601. Next, the number of pits in the same measured field of view (area of ​​100 µm) is determined. 2 ) counted. The scale for assessing the pits is defined as follows. That is, among the depressions observed on the surface, the pit is defined as follows. (1) The depression has a Φ of 50 nm or more and 2000 nm or less. (2) The depth of the depression is 1 nm or more.

[0029] According to the present invention, the arithmetic mean roughness Ra of the surface of the vibrating plate and the surface (surface on which the bonding layer is formed) of the high-strength ceramic plate are set to 0.01 nm or more and 10.0 nm or less, respectively, and can preferably be set to 7.0 nm or less and more preferably to 5.0 nm or less with regard to flexural strength. Furthermore, Ra is 0.01 nm or more and more preferably 0.02 nm or more when it comes to adhesion to the bonding layer.

[0030] Furthermore, the pit density of the surface of the vibrating plate is 10 or more, preferably 20 counts or more, per 100 µm². 2Furthermore, the pit density of the surface of the vibrating plate is typically 200 counts or less, preferably 96 counts or less, and particularly preferably 70 counts or less per 100 µm². 2 .

[0031] It is assumed that the pits on the surfaces of the vibrating plate and the high-strength ceramic plate facing the bonding layer are caused by the sintering aid added for dense sintering of the high-strength ceramic plate. A significant portion of the excess sintering aid remains after sintering as aggregates in the intergranular boundaries between the ceramic grains. If the high-strength ceramic is formed into a wafer with the remaining sintering aid and then polished to a mirror surface, the polishing rate is higher in the areas where the sintering aid is aggregated than in the areas consisting of the high-strength ceramic itself. The pits form in these aggregated areas.There is therefore a relationship between the amount of sintering aid added and the number of pits, so that it is possible to regulate the number of pits by adjusting the amount of sintering aid added.

[0032] From the perspective of achieving the required bond strength and low Ra of the high-strength ceramic plate, the relative density of the high-strength ceramic plate can preferably be 95% or higher and more preferably 99% or higher. The type and amount of sintering aid suitable for achieving the Ra and pit densities described above are selected according to the type of high-strength ceramic to be sintered. The sintering aid can be, for example, Y₂O₃, CaO, MgO, or ZrO₂.

[0033] According to the present invention, the arithmetic mean surface roughness Ra of the back surfaces (surfaces on which the bonding layer is not formed) of the vibration plate and the high-strength ceramic plate can preferably be 0.01 nm or more and 10.0 nm or less, from the point of view of adhesion strength.

[0034] Regarding the process for polishing the surface of the high-strength ceramic plate, for example, after grinding to the desired thickness with a #3000 grinding stone, it is lapped with a diamond suspension with a grain size of 3 µm and refined to a mirror surface by chemical-mechanical polishing (CMP).

[0035] Although the thickness of the bonding layer 2 formed as a film on the high-strength ceramic plate is not particularly limited, from the point of view of production costs the thickness can preferably be 0.01 to 10 µm and more preferably 0.05 to 0.5 µm.

[0036] Although the method for film formation of the bonding layer 2 is not limited, the sputtering method, the chemical vapor deposition (CVD) method and the vapor deposition method are mentioned as examples.

[0037] The method for leveling the bonding surface of bonding layer 2 and the bonding surface of the support substrate can be lapping, chemical-mechanical polishing (CMP) or the like.

[0038] In a preferred embodiment, the surface 2b of the bonding layer 2 and the surface 3a of the support substrate 3 can be activated by neutralized atomic beams. Particularly in the case that the surface 2b of the bonding layer 2 and the surface 3a of the support substrate 3 are planar surfaces, direct bonding can be easily achieved.

[0039] When surface activation is achieved using the neutralized beam, a system for generating the neutralized beam, as described in patent document 2, is preferably employed. This system utilizes a high-speed saddle-field atomic beam source. An inert gas is then introduced into the chamber, and a high voltage from a direct current source is applied to the electrodes. This generates a saddle-field electric field between the electrode (positive electrode) and a housing (negative electrode), causing electrons to move, thus generating atomic and ion beams from the inert gas. Of the beams reaching a grating, the ion beam is neutralized at the grating, and the beam of neutral atoms is emitted from the high-speed atomic beam source.The atomic species that provides the beam can preferably be an inert gas (argon, nitrogen or the like).

[0040] In the activation step by radiation irradiation, the voltage can preferably be 0.5 to 2.0 kV and the current preferably 50 to 200 mA.

[0041] The activated surfaces are then brought into contact and bonded under a vacuum atmosphere. The temperature at this point can be ambient temperature, in particular 40°C or less, and preferably 30°C or less. Furthermore, the temperature during bonding can preferably be 20°C or higher and 25°C or lower. The pressure during bonding is preferably 100 to 20,000 N.

[0042] The high-strength ceramic plate is then processed to achieve a thickness of 100 µm or less. Since the thickness of the vibratory plate is selected based on the target frequency, the lower limit of the thickness is not particularly restricted, and the thickness can preferably be 1 µm or greater to facilitate processing. Regarding the processing method, for example, after grinding with a 3 µm diamond suspension, it is lapped to the desired thickness using a #3000 grinding wheel and subsequently finished to a mirror surface by chemical-mechanical polishing (CMP). EXAMPLES (Examples of the invention 1 to 8)

[0043] The vibration plate composite body was, as in the Fig. 1 and Fig. 2 described, manufactured.

[0044] In particular, a Sialon wafer-shaped high-strength ceramic substrate 1 with a diameter of 4 inches and a thickness of 250 µm was used. Each surface 1a of each high-strength ceramic plate 1 was ground to the desired thickness using a #3000 grinding wheel. In the case of the surface of the vibratory plate shown in Table 1 (Ra ≤ 1 nm), the surface was lapped with a 3 µm diamond suspension and subsequently finished to a mirror surface by chemical-mechanical polishing (CMP), such that the arithmetic mean roughness Ra was set to each numerical value given in Tables 1, 2, and 3. The pressure and processing time during CMP polishing were adjusted to achieve the desired Ra values. In the case of the vibratory plate surface shown in Table 2 (Ra > 1 nm), the surface was lapped to a mirror surface with a diamond suspension.To adjust the numerical value of Ra, the grain size of the diamond suspension used for finishing was chosen in a range of 0.5 µm to 6 µm.

[0045] Furthermore, the surface roughness (Ra) of surface 1a of the high-strength ceramic vibrating plate 1 was measured in a 10 µm × 10 µm field of view using an atomic force microscope (AFM). Additionally, the number of pits with a diameter of 50 nm or larger was counted using an atomic force microscope (AFM) in a 10 µm × 10 µm field of view. When measuring the number of pits on surface 1a of the high-strength ceramic plate 1, the number of pits was measured at three locations: the central point of the wafer-shaped plate 1, the point within a 10 mm alignment plane of the plate 1, and the point within 10 mm of the end opposite the alignment plane of the plate 1. The mean of the values ​​measured at these three points was defined as the pit density, which is given in Table 1, 2, or 3.

[0046] Furthermore, it shows Fig.3 the condition of the surface of the high-strength ceramic plate used in the inventive example 4 (Ra=0.07 nm, pit density in the field of view of 10 µm × 10 µm = 58 counts).

[0047] Furthermore, the flexural strength of each of the high-strength ceramic plate examples could not be measured in the substrate after bonding. Therefore, each high-strength ceramic plate 1 was manufactured with the same material, thickness, pit density, and Ra as each of the high-strength ceramic plate examples 1, and each test piece was cut from each of the high-strength ceramic plates and subjected to three-point flexural strength measurement. The flexural strength was measured according to the three-point flexural strength standard described in JISR 1601 (Method for testing the flexural strength of fine ceramics at room temperature). Regarding the size of the test piece, the length, width, and thickness of the piece were 40.0 mm, 4.0 mm, and 3.0 mm, respectively.

[0048] The bonding layer 2 was then deposited onto the surface 1a of the high-strength ceramic plate 1 by direct current sputtering. Boron-doped silicon was used as the target. The thickness of the bonding layer 2 was adjusted to 30 to 200 nm. The arithmetic mean roughness Ra of the surface 2a of the bonding layer 2 was 0.2 to 0.6 nm. The bonding layer 2 was then subjected to chemical-mechanical polishing (CMP) to increase the film thickness to 20 to 150 nm and Ra to 0.08 to 0.4 nm.

[0049] The substrate 3, consisting of an alignment plane (OF) with a diameter of 4 inches and a thickness of 500 µm, was made of silicon. The surface of the substrate 3 was treated by chemical-mechanical polishing (CMP), resulting in a mean arithmetic roughness Ra of 0.2 nm.

[0050] After the surface 2b of the bonding layer 2 and the surface 3a of the support substrate 3 had been cleaned of contaminants, the substrate was placed in a vacuum chamber. After evacuation on the order of 10 -6 The respective surfaces were irradiated with a high-speed atomic beam for 120 seconds (acceleration voltage of 1 kV and Ar flux rate of 27 sccm). After the activated surface 2b of the bonding layer 2 and the activated surface 3a of the support substrate 3 had been brought into contact, the substrates were bonded together under a pressure of 10,000 N for 2 minutes ( Fig. 2(a)). The bonded bodies of the respective examples were heated at 100°C for 20 hours.

[0051] Then the back surface 1b of the high-strength ceramic plate 1 was ground and polished, from an original 250 µm to 40 µm (see Fig. 2(b)). Table 1 Example according to the invention 1 Example 2 according to the invention Example according to the invention 3 Example according to the invention 4 materials Vibration plate Sialon Sialon Sialon Sialon Bonding layer α-Si α-Si α-Si α-Si carrier substrate Si Si Si Si Number of pits on the surface of the vibration plate (counts) 10 45 96 58 Ra on the surface of the vibration plate (nm) 0,02 0,03 0,04 0,07 Peeling off the vibratory plate and the carrier substrate during the processing of the vibratory plate No peeling occurs with a thickness of 40µm of the vibrating plate. No peeling occurs with a thickness of 40µm of the vibrating plate. No peeling occurs with a thickness of 40µm of the vibrating plate. No peeling occurs with a thickness of 40µm of the vibrating plate. Flexural strength of the vibration plate (MPa) 705 700 695 690 Table 2 Example according to the invention 5 Example according to the invention 6 Example according to the invention 7 Example according to the invention 8 materials Vibration plate Sialon Sialon Sialon Sialon Bonding layer α-Si α-Si α-Si α-Si carrier substrate Si Si Si Si Number of pits on the surface of the vibration plate (counts) 53 12 55 94 Ra on the surface of the vibration plate (nm) 4,98 9,97 9,96 9,94 Peeling off the vibratory plate and the carrier substrate during the processing of the vibratory plate No peeling at a thickness of 40µm vibrating plate No peeling at a thickness of 40µm vibrating plate No peeling at a thickness of 40µm vibrating plate No peeling at a thickness of 40µm vibrating plate Flexural strength of the vibration plate (MPa) 640 500 500 500 Table 3 Comparative example 1 Comparative example 2 Comparative example 3 structure Vibration plate Sialon Sialon Sialon Bonding layer - α-Si α-Si carrier substrate Si Si Si Number of pits on the surface of the vibration plate (counts) 51 4 55 Ra on the surface of the vibration plate (nm) 0,03 0,01 10,85 Peeling off the vibratory plate and the carrier substrate during the processing of the vibratory plate Peeling at a thickness of 110 µm of the vibration plate Peeling at a thickness of 100 µm of the vibration plate No peeling occurs with a vibration plate thickness of 40 µm. Flexural strength of the vibration plate (MPa) - - 300

[0052] According to examples 1 to 8 of the invention, peeling was completely prevented at a pit density of 10 to 96 counts and an Ra of 0.02 to 9.97 nm, even when the vibratory plate 1A was polished to a thickness of 40 µm. Although the flexural strength of the ceramic tends to be lower as the Ra increases, a sufficient flexural strength of 500 MPa was demonstrated even when the Ra was 9.97 nm. (Comparative example 1]

[0053] According to Comparative Example 1, the α-Si bonding layer 2 was not formed as a film on the high-strength ceramic plate 1. Instead, a high-velocity atomic beam was directed onto the surface 1a of the high-strength ceramic plate 1, and the activated surface 1a of the high-strength ceramic plate 1 and the activated surface 3a of the support substrate 3 were brought into contact and bonded to form a composite body. However, the pit count and surface area (Ra) of the surface 1a of the high-strength ceramic plate 1 in Comparative Example 1 were 51 counts and 0.03 nm, respectively. Furthermore, it was produced under the same conditions as in the inventive Example 1, except that the α-Si bonding layer was not film-formed.

[0054] The back surface 1b of the high-strength ceramic plate 1 of the composite body thus obtained was then ground and polished, reducing its thickness from the original 250 µm. When the thickness of the high-strength ceramic plate 1 reached 110 µm, peeling was observed at the bonding interface between the high-strength ceramic plate and the support substrate. The cause of the peeling is described below. The bond strength between the high-strength ceramic plate 1 and the support substrate 3 of the composite body was lower than the bond strengths achieved in Examples 1 to 8 according to the invention, so that the composite body could not withstand the machining stresses during the polishing of the high-strength ceramic plate 1. (Comparison examples 2 and 3]

[0055] The respective composite bodies of comparative examples 2 and 3 were produced under the same conditions as those of examples 1 to 8 according to the invention.

[0056] In comparative example 2, however, the number of pits on surface 1a of the high-strength ceramic plate 1 was only 4, and the surface roughness (Ra) of surface 1a was specified as 0.01 nm. In this case, where the back surface of the high-strength ceramic plate 1 was thinned to a thickness of 100 µm by grinding and polishing, peeling was observed at the interface between the surface of the high-strength ceramic plate 1 and the surface of the bonding layer 2. It is assumed that the bond strength of the high-strength ceramic plate 1 and the bonding layer 2 could not withstand the machining loads applied during the polishing of the high-strength ceramic plate 1.

[0057] Furthermore, according to examples 1 to 4 of the invention, peeling was not observed even when the surface roughness (Ra) at the ceramic interface was less than 0.2 nm and sufficiently low. It is assumed that the pits were present on the surface 1a of the high-strength ceramic plate 1 and that the bonding layer 2 formed as a film over the pits has an anchoring effect to improve the adhesive strength.

[0058] According to comparative example 3, the number of pits on surface 1a of the high-strength ceramic vibratory plate 1 was 55, but the surface roughness (Ra) on surface 1a was 10.85 nm. In the case where Ra was 10.85 nm, the flexural strength of the high-strength ceramic plate was reduced to 300 MPa. It is assumed that a load is concentrated on the surface roughness of the high-strength ceramic plate, thereby reducing the flexural strength.

Claims

[1] Vibration plate composite body (5) comprising: a silicon-containing support substrate (3); a vibrating plate (1A) comprising a high-strength ceramic and having a thickness of 100 µm or less; and a bonding layer (2) between the support substrate (3) and the vibrating plate (1A), which touches a surface (1a) of the vibrating plate (1A) and comprises α-Si, wherein the surface (1a) of the vibrating plate (1A) has an arithmetic mean roughness Ra of 0.01 nm or more and 10.0 nm or less, and wherein the surface (1a) of the vibrating plate (1A) has a pit density of 10 counts or more per 100 µm 2 exhibits. [2] Vibration plate composite body (5) according to claim 1, wherein the bonding layer (2) and the support substrate (3) are directly bonded together. [3] Vibration plate composite body (5) according to claim 1 or 2, wherein the high-strength ceramic is selected from the group consisting of sialon, cordierite, mullite, translucent aluminium oxide, aluminium nitride, silicon nitride and silicon carbide. [4] Vibration plate composite body (5) according to any one of claims 1 to 3, wherein the surface (1a) of the vibration plate (1A) has a pit density of 200 counts or less per 100 µm 2 exhibits. [5] Method for producing a vibratory plate composite body (5) wherein the method comprises the steps: Provision of an α-Si-comprising bonding layer (2) on a surface (1a) of a high-strength ceramic plate (1) made of a high-strength ceramic; subsequent bonding of a bonding surface (2a, 2b) of the bonding layer (2) and a bonding surface (3a) of a silicon-comprising support substrate (3); and subsequent processing of the high-strength ceramic plate (1) to obtain a vibratory plate (1A) with a thickness of 100 µm or less, wherein the surface (1a) of the high-strength ceramic plate (1] has an arithmetic mean roughness Ra of 0.01 nm or more and 10.0 nm or less, and wherein the surface (1a) of the high-strength ceramic plate (1) has a pit density of 10 counts or more per 100 µm 2 exhibits. [6] Method for producing a vibratory plate composite body (5) according to claim 5, wherein the method further comprises the step of direct bonding of the bonding surface (2a, 2b) of the bonding layer (2) and the bonding surface (3a) of the support substrate (3). [7] Method for producing a vibratory plate composite body (5) according to claim 6, wherein the method further comprises the step of activating the bonding surface (2a, 2b) of the bonding layer (2) and the bonding surface (3a) of the support substrate (3) by a neutralized atom beam (A, B), wherein the bonding surfaces (2a, 2b, 3a) are then directly bonded together. [8] Method for producing a vibratory plate composite body (5) according to any one of claims 5 to 7, wherein the high-strength ceramic is selected from the group consisting of sialon, cordierite, mullite, translucent aluminium oxide, aluminium nitride, silicon nitride and silicon carbide. [9] Method for producing a vibratory plate composite body (5) according to any one of claims 5 to 8, wherein the surface (1a) of the high-strength ceramic plate (1) has a pit density of 200 counts or less per 100 µm 2 exhibits.

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