JP4324948B2 - Manufacturing method of high-frequency piezoelectric vibration device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a piezoelectric vibration device such as a crystal resonator and a crystal filter used as a receiving unit of a communication device or a clock source of a microcomputer, and particularly relates to a piezoelectric vibration device that is thin and compatible with high frequency.
[0002]
[Prior art]
With the increase in frequency of communication equipment or the increase in the operating frequency of microcomputers, piezoelectric vibration devices such as crystal resonators and crystal filters are also required to support higher frequencies. In general, the thickness shear vibration of an AT-cut quartz plate is often used as a quartz plate corresponding to a higher frequency, and as is well known, the frequency is determined by the thickness, and the frequency and the thickness are inversely proportional. For example, when a fundamental vibration frequency of 100 MHz is obtained, an ultrathin piezoelectric diaphragm having a thickness of about 16 μm is required. Such processing of an ultra-thin plate is difficult to polish and it has been difficult to improve the manufacturing yield.
[0003]
In order to solve such a problem, as shown in FIG. 6 (f), a concave portion is provided in the center portion of the quartz plate, and a thinned vibration region 91 is set at the bottom portion of the concave portion. A configuration having a reinforcing portion 92 that reinforces the vibration region at a portion has been invented. FIG. 6F is an internal cross-sectional view showing a conventional example. In the quartz plate 9 having the vibration region 91 of the thinned recess and the thick reinforcing portion 92 formed around the vibration region 91, a plurality of vibration regions 91 are provided in the vibration region 91. The excitation electrode 9a is formed, and although not shown, the electrode is drawn from the concave portion to the end of the thick portion. By adopting such a configuration, the overall mechanical strength can be maintained and the vibration region can be made much thinner than the conventional one. Compared to the conventional single-thick piezoelectric diaphragm described above, 16 μm or The vibration region having a thickness smaller than that could be formed with a good yield.
[0004]
In order to obtain a piezoelectric vibrator having such a configuration, for example, a manufacturing process using a photolithography technique as shown in FIGS. As shown in FIG. 6A, a Cr film 93 and an Au film 94 are sequentially formed on the front and back surfaces (both main surfaces) of the quartz plate 9 as a protective film by a vacuum deposition method or the like. As shown in FIG. 6B, after a resist solution is applied to the surface (one main surface) on which the recesses are formed, patterning exposure is performed to obtain a resist film 95 having a predetermined pattern. Using this resist film 95 as a mask, a part of the Au film and Cr film, which are protective films, are etched to obtain a protective film having a pattern corresponding to the recess. Thereafter, the resist film is removed, and as shown in FIG. 6D, a part of the crystal plate is etched using the protective film as a mask to form a recess. Then, after peeling off and removing the protective film, an excitation electrode is formed as shown in FIG.
[0005]
[Problems to be solved by the invention]
According to the manufacturing method described above, it is necessary to form a protective film on the main surface of the quartz plate on which the concave portion is not formed. This protective film is finally formed together with the protective film used for forming the concave portion in the actual manufacturing process. Will be removed. The thickness of the protective film is determined by the required frequency, that is, the etching time of the quartz plate. For example, the Au film requires several hundred to several thousand angstroms, but these are eventually removed, which increases the manufacturing cost.
[0006]
In order to perform etching efficiently without variation during etching, etc., it is necessary to place the crystal plate in a jig with a predetermined interval and immerse it in an etching solution. There was also a problem that it was limited and reduced the mass production efficiency.
[0007]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method of manufacturing a high-frequency piezoelectric vibrating device that can suppress manufacturing costs and increase manufacturing efficiency.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides a central portion by forming a recess in the central portion of one main surface of an AT-cut quartz plate whose frequency is determined by the thickness, as shown in claim 1. A method of manufacturing a high-frequency piezoelectric vibration device in which a thin piezoelectric vibration region is formed and a thick reinforcing portion provided around the piezoelectric vibration region is formed. Etching solution in a state where main surfaces not forming recesses are bonded to each other , a metal protective film is formed on the bonding surfaces, and masking is performed so that predetermined recesses are formed on the main surfaces forming the recesses. The two AT-cut quartz plates are separated after being dipped in to form a recess.
[0009]
With the above structure, the corrosion resistance due to the etching solution can be improved on the bonding surface.
[0010]
Alternatively, a configuration may be employed in which an adhesive used for bonding is wrapped around the end surface of the bonding surface to prevent penetration of the etching solution into the bonding portion.
[0011]
According to the present invention , only the main surface necessary for forming the recess can be etched by bonding the two piezoelectric diaphragms together. Therefore, it is not necessary to form a protective film such as an Au film on the other main surface that is not involved in the formation of the recess as in the prior art.
[0012]
In addition, since the piezoelectric diaphragm integrated into one set at the time of forming the resist film and the protective film or etching is used, handling in manufacturing becomes easy, and manufacturing efficiency can be improved.
[0013]
Embodiment
The first embodiment of the present invention will be described with reference to the drawings, taking an MCF (monolithic crystal filter) using an AT-cut quartz plate as an example.
[0014]
FIG. 1 is a view showing a manufacturing method according to the present invention, and FIG. 2 is a perspective view showing a large wafer processed so as to obtain a large number of crystal plates.
FIG. 1 shows a manufacturing process from using two quartz plates to forming electrodes after forming recesses in both plates. In FIG. 1A, the main surfaces of the quartz plate 1 and the quartz plate 2 that do not form the recesses are bonded together with the adhesive 3, and then the metal films (protective films) 10 and 20 are formed on the main surfaces other than the bonded surfaces. The formed state is shown. The quartz plates 1 and 2 have a thickness of about 50 μm, and both main surfaces thereof are mirror-finished by polishing. In this embodiment, the novolac polymer resin is used as the adhesive 3. However, the adhesive 3 may be an acrylate-based or hydroxystyrene-based polymer resin, an epoxy-based adhesive, UV ( It may be an ultraviolet) curable adhesive. The metal films 10 and 20 are formed by using a thin film forming means such as a vacuum deposition method, Cr films 11 and 21 are formed in contact with the crystal plates 1 and 2, and Au films 12 and 22 are formed on the upper surfaces thereof.
[0015]
FIG. 1B shows the formation of a resist film formed on the surface of the metal film. In this example, a positive type of OFPR-800 manufactured by Tokyo Ohka Kogyo Co., Ltd. is used as the resist film. A photoresist is uniformly coated on the metal films 10 and 20 by a spinner or the like and exposed through a photomask having a predetermined mask pattern (not shown). Thereafter, an unnecessary resist 41 is removed through a development process or the like, and a resist film 4 having a predetermined mask pattern is obtained.
[0016]
Thereafter, part of the metal films 10 and 20 is etched using the resist film 4 as a mask to obtain metal films 10a and 20a having a mask pattern for forming the recesses 1a and 2a in the crystal plate. FIG. 1C shows a state in which the concave portions 1a and 2a are formed in the quartz plate by etching using the patterned metal films 10a and 20a as a mask. The etching depth of the recess is controlled by parameters such as the type of etching solution, the surrounding environment, and the etching time. In this example, etching is performed for about 4 hours using a mixed solution of hydrofluoric acid and ammonium fluoride as the etching solution. As a result, an etching amount of about 35 μm is obtained. As a result, the thin piezoelectric vibration region of the recess has a thickness of about 15 μm.
[0017]
In FIG. 1D, after the etching is completed, the metal films 10a and 20a are removed by immersing them in a metal stripping solution, and the adhesive 3 is removed by immersing them in a resin stripping solution. The separated state is shown. As a result, two quartz plates having thick reinforcing portions 13 and 23 and thin piezoelectric vibration regions 14 and 24 can be obtained.
[0018]
Thereafter, as shown in FIG. 1E, excitation electrodes and extraction electrodes (not shown) are formed in the piezoelectric vibration regions 14 and 24. In this example, in order to obtain MCF, the divided electrodes 15, 16, 25, 26 and the common electrodes 17, 27 are formed as excitation electrodes by a vacuum deposition method using a masking means.
[0019]
In the above manufacturing example, an example in which two quartz plates are attached is shown. However, in actual manufacturing, a large wafer is often used for batch processing from the viewpoint of efficiency. FIG. 2 shows an example in which two large crystal wafers W1 and W2 are bonded together to obtain a large number of crystal plates 1 having recesses 10, and deep grooves W11 and W21 for splitting are vertically and horizontally around each crystal plate. Is formed. Of course, it is possible to cut the wafer into pieces by dicing or the like without forming the deep groove.
[0020]
A second embodiment will be described with reference to FIG. Note that the same structural parts as those described in the above embodiment are described using the same reference numerals, and part of the description of the same configuration and manufacturing method is omitted.
[0021]
In this example, two crystal plates 1 and 2 are attached to face the holding plate 5. For the holding plate, a material having corrosion resistance against an etching solution such as Pt or Au is used. Alternatively, the core portion may be made of graphite and the surface thereof may be plated with high-purity SiC, or the quartz may be made of a core and Cr—Au may be plated to provide corrosion resistance to the etching solution. As shown in FIG. 3A, positioning recesses 51 and 52 are formed on the front and back surfaces of the holding plate 5 in a cross section. The quartz plates 1 and 2 are bonded to the positioning recesses by adhesives 61 and 62, and metal films 10 and 20 made of Cr films 11 and 21 and Au films 12 and 22, respectively, are formed. This positioning recess is not essential, but functions effectively for positioning and fixing in manufacturing. As shown in FIG. 3B, a resist film 4 is formed, and the metal films 10 and 20 are etched into a predetermined pattern using the resist film 4 as a mask. Thereafter, etching is performed using the patterned metal films 10a and 20a as a mask as shown in FIG. 3C to form recesses 1a and 2a in the quartz plate.
[0022]
After the etching is finished, as shown in FIG. 3D, the metal films 10a and 20a are peeled off and the adhesives 61 and 62 are peeled off to separate the quartz plates 1 and 2 from the holding plate 5. Thereafter, an excitation electrode is formed on the quartz plate having the separated recesses. In this embodiment, since a crystal resonator is illustrated, excitation electrodes 71 and 72 and extraction electrodes (not shown) are formed on the front and back sides of the piezoelectric vibration region as shown in FIG.
[0023]
In each of the embodiments described above, an example in which quartz plates having the same outer size are bonded is shown. However, quartz plates or quartz wafers having different sizes may be bonded. In this case, it is possible to perform flexible manufacturing, such as being able to handle multi-product production. However, it is necessary to form a protective film (resin or metal film) against etching on the protruding region of the bonded surface of the crystal plate or crystal wafer having a large outer size.
[0024]
Further, in order to prevent the etching solution from penetrating into the bonded portion, as shown in FIG. 4, after forming thin metal films 18 and 28 as protective films on the bonded surfaces of the crystal plates 1 and 2, an adhesive is used. A crystal plate may be bonded together by 3. In order to reduce the cost of the metal film material, the protective film may be formed only in the vicinity of the outer periphery of the bonded surface of the crystal plate.
[0025]
Further, as shown in FIG. 5, in the vicinity of the outer periphery of the adhesive bonding, by applying the adhesive 3 so as to cover the side surfaces of the bonded quartz plates 1 and 2 (illustrated by 29), the quartz plate is etched. Unintentional corrosion of the bonding surface can be prevented. The side surface coating needs to include at least a circumferential bonded portion.
[0026]
In each of the above embodiments, the quartz plate is exemplified as the piezoelectric body, but other piezoelectric bodies such as lithium tantalate and langasite may be used.
[0027]
【The invention's effect】
According to the present invention , only the main surface necessary for forming the recess can be etched by bonding the two piezoelectric diaphragms together. Accordingly, it is not necessary to form a protective film such as an Au film having a film thickness that can sufficiently withstand the etching solution in direct contact with the other main surface that is not involved in the formation of the recess as in the prior art. Therefore, the material cost at the time of manufacture can be reduced.
[0028]
In addition, since the piezoelectric diaphragm integrated into one set at the time of forming the resist film and the protective film or etching is used, handling in manufacturing is facilitated, and manufacturing efficiency can be improved.
[Brief description of the drawings]
FIG. 1 shows a manufacturing process according to the present invention.
FIG. 2 is a view showing a manufacturing method according to the present invention.
FIG. 3 is a view showing a manufacturing method according to the present invention.
FIG. 4 is a view showing a manufacturing method according to the present invention.
FIG. 5 is a view showing a manufacturing method according to the present invention.
FIG. 6 is a diagram showing a conventional example.
[Explanation of symbols]
1, 2, 9 Crystal plate (piezoelectric vibration device)
10, 20 Metal film 1a, 2a Recess 14, 24, 91 Piezoelectric vibration region 13, 23, 92 Reinforcement part 15, 16, 17, 25, 26, 27, 71, 72, 9a Excitation electrode 4 Resist film W1, W2 Quartz Wafer

Claims (1)

By forming a recess in the central part of one main surface of the AT-cut quartz plate whose frequency is determined by the thickness, a thin piezoelectric vibration area is formed in the central part and provided around the piezoelectric vibration area. Manufacturing method of a high-frequency piezoelectric vibration device formed by forming a thick reinforcing portion, and bonding main surfaces of two AT-cut quartz plates that do not form a recess to each other, and protecting the bonded surface with metal After forming a film and masking so that a predetermined recess is formed on the main surface where the recess is formed, the two AT-cut quartz plates are separated after forming the recess by dipping in an etching solution. A method for manufacturing a high-frequency piezoelectric vibration device.

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