JP2002314162A - Crystal substrate and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rectangular piezoelectric substrate, capable of accurately measuring a resonance frequency of a high-frequency crystal substrate and to provide a method for manufacturing the piezoelectric substrate. SOLUTION: The high-frequency crystal substrate is obtained by obliquely polishing the four peripheral edges of one main surface of an AT cut crystal substrate by a width (a) and a thickness (t) in such a manner that a ratio 2a/L of twice of the width (a) of the peripheral edge to the long side L of the rectangular substrate is set to substantially 0.1. The method for manufacturing the piezoelectric substrate comprises the steps of forming a protective film having a lattice-like exposure part of a predetermined width by vapor-depositing or adhering by sputtering gold thin films on both side surfaces of the AT cut crystal substrate, and patterning the gold thin films. The method further comprises the steps of then dipping the film in an etching liquid, etching the film to a desired depth, then separating the protective film of gold, and cutting the film to obtain the AT cut crystal substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric substrate, and more particularly to a high-frequency quartz substrate capable of measuring a resonance frequency of the piezoelectric substrate with high accuracy.

[0002]

2. Description of the Related Art A piezoelectric substrate, for example, a quartz substrate is processed into a quartz oscillator or a quartz filter, and is used in almost all electronic devices. In particular, piezoelectric devices have greatly contributed to the spread of mobile phones in recent years, and have become indispensable electronic devices for generating stable frequencies and selecting necessary frequencies. The shape of the quartz substrate greatly depends on the desired frequency. In the low frequency band of 10 MHz or less, a planoconvex substrate in which one main surface is polished into a lens shape and the other main surface is polished into a planar shape, and both main surfaces are formed into a lens shape A biconvex substrate that has been machined, or a bevel substrate that has a chamfered edge of the substrate is used. In the frequency band of 10 MHz or more, a flat crystal substrate is generally mainly used,
When the frequency is about 70 MHz or more, the substrate becomes thin, and processing and handling become difficult. Therefore, a high-frequency crystal substrate in which a recess is formed on one main surface of the crystal substrate and the other surface is flat has been developed and put to practical use.

FIG. 6A is a view for explaining a process of forming a high-frequency quartz substrate, in which a gold thin film is formed on the entire surface of a large AT-cut quartz substrate (wafer) 21 formed into a thin plate of about 80 μm. Then, a resist film is applied on the thin film, and the resist film is exposed through a mask (masking). When the exposed resist film is stripped using a stripping agent, a gold thin film whose exposed shape is arranged in a matrix form is exposed. After dissolving the gold thin film in aqua regia or the like, exposing the quartz substrate surface, immersing the exposed surface in an etching solution containing ammonium fluoride as a main component and etching, and then removing the resist film, As shown in FIG. 6A, a wafer 21 in which individual substrates 22 each having a recess on one surface are arranged in a matrix is obtained. At this time, the dividing etching grooves 23, 23, 23
・ Also formed vertically and horizontally at the same time. When a knife edge is applied to the opposite side of the groove and folded, a quartz substrate having a concave portion 24 on the main surface as shown in FIG. 6B is obtained. FIG. 7 is a flowchart showing the above process.

Further, the resonance frequencies of the individual piezoelectric substrates 22 arranged in a matrix are measured by using an air gap type apparatus having upper and lower electrodes as shown in FIG. Is within a predetermined frequency range. When the resonance frequency is lower than the predetermined range, in order to adjust the resonance frequency to the predetermined frequency, the etching time is controlled by dripping an etchant into each recess using a computer-controlled device. Thereby, the frequency of each piezoelectric substrate 22 is finely adjusted.
For this reason, a structure in which the thin portion, which is the vibrating portion, is surrounded by a higher wall surface is required. FIG. 6B is an enlarged perspective view of the piezoelectric substrate 22 obtained by dividing the wafer 21 into individual pieces along the etching grooves 23, and includes a thin portion 24 serving as a vibrating portion and an annular surrounding portion holding the thin portion 24. 25 are integrally formed. FIG.
(C) is a sectional view taken along QQ.

However, in recent mobile phones, the vibration device has been required to be further reduced in size, and the annular surrounding portion (outer edge) 25 shown in FIG.
Therefore, in consideration of the improvement of the processing accuracy of the thin plate of the polishing machine, a large flat AT-cut quartz substrate (wafer) is polished to a predetermined frequency and cut with a dicing saw to obtain individual piezoelectric substrates. The frequency fine adjustment was adjusted by etching.

[0006]

However, when the frequency of the quartz substrate is measured by an air gap method as shown in FIG. 8 as the quartz substrate becomes thinner, the frequency spectrum (resonance waveform) becomes as shown in FIG. There are many phenomena in which it cannot be determined which peak the true resonance is at. When the maximum value of the frequency spectrum is classified as the true value of the resonance frequency, an electrode is attached to the quartz substrate, and the resonance frequency is measured, the frequency may be significantly different from a predetermined frequency. With the shape described above, there was a problem that the frequency of the quartz substrate could not be measured accurately. The present invention has been made to solve the above-described problem, and has as its object to provide a piezoelectric substrate capable of accurately measuring a resonance frequency of a high-frequency piezoelectric substrate.

[0007]

In order to achieve the above object, a quartz substrate according to the present invention and a method of manufacturing the same according to the present invention are characterized in that at least one main surface of at least one main surface of a rectangular AT-cut quartz substrate is provided. A high-frequency crystal substrate whose periphery is half-etched to a predetermined depth, wherein the relationship between the width a of the half-etched portion and the long side L of the substrate is 2a / L ≒
It is a quartz substrate characterized by satisfying 0.1. The invention according to claim 2 is a step of forming a protective film having a lattice-shaped exposed portion having a predetermined width on at least one surface of the AT-cut quartz wafer, and a step of wet-etching the exposed quartz wafer to a desired depth. And a step of cleaning the wafer and stopping the etching, and a step of removing the protective film.
Cutting the wafer along the etched portion into individual pieces.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the drawings. 1 (a), (b),
(C) is a diagram showing a configuration of a rectangular AT-cut quartz substrate according to the present invention, in which (a) is a plan view, (b) is a cross-sectional view of the length L in the Z′-axis direction, FIG. 3C is a cross-sectional view of the length L ′ in the X-axis direction. As shown in the left end of the figure, the coordinate axes of the quartz substrate are in the thickness direction, that is, the Y'-axis direction in the cross-sectional views of FIGS. 1B and 1C.
As shown in FIG. 1A, half-etching is performed on four peripheral edges of one main surface of a rectangular flat plate by a width a and a depth t. Here, half etching refers to etching to a predetermined depth so as not to penetrate in the thickness direction. As a polishing means, a polishing method by wet etching suitable for batch processing is used. However, due to the anisotropy of the piezoelectric substrate, the etched sectional shape of each side is slightly different. FIG.
(A) and (b) schematically show a cross section of an AT-cut quartz substrate, and an etching cross section is taken along the Z ′ axis and the X axis.
That is, the etching inclined surface is different. Note that the polishing depth t strictly depends on the thickness of the substrate, that is, the frequency of the substrate. However, when operating at 40 MHz or more in the fundamental wave, the polishing may be performed by about 1 μm.

FIG. 1 (d) is a diagram showing a case where the width a of the polished portion of the periphery of an AT-cut quartz substrate obtained by half-etching four edges as shown in FIGS. The ratio 2a / L to the long side L of the substrate (L ≧ L ′) is set to approximately 0.
FIG. 9 is a diagram of measuring a frequency spectrum in the vicinity of the resonance frequency of the high-frequency crystal substrate in the case of about 1 by the air gap method shown in FIG. 8. Is shown.

FIG. 2 is a view showing the structure of another embodiment of the AT-cut quartz substrate, and is a view showing a cross section in the X-axis direction. When the four peripheral edges of both main surfaces are etched shallowly, the cross sections are etched into different shapes due to anisotropy. Strictly, the etching depth t ′ on one side should be determined based on the thickness of the quartz substrate. However, if the fundamental wave is 40 MHz or more, the resonance spectrum of the quartz substrate is reduced by about 0.5 μm to obtain Good waveform is obtained.
The example shown in FIG. 2 has a point-symmetric shape with respect to the center of the figure.

FIGS. 3 (a), 3 (b) and 3 (c) are views showing steps for producing an AT-cut quartz substrate having the shape shown in FIG. A gold thin film is attached to both sides of the AT-cut quartz wafer using a vapor deposition device or a sputtering device, and a resist film is applied on the thin film. Then, the resist film is exposed through a mask having a lattice pattern, and the exposed portion of the resist film is stripped using a stripping agent. Then, the gold thin film is exposed from the gaps of the resist films arranged in a matrix form, so that the exposed gold thin film is dissolved in aqua regia or the like, and then the resist film is peeled off. Can be formed. FIG.
(A) is a cross-sectional view of a crystal wafer provided with a protective film on one main surface. FIG. 3 shows a state in which the lattice-shaped exposed portion is immersed in an etching solution containing ammonium fluoride as a main component and half-etched (etching depth t) to a desired depth.
The sectional view shown in FIG. Further, when the gold protective film is peeled off, a quartz wafer having small shallow lattice-shaped grooves on one main surface as shown in FIG. 3C is obtained. When the quartz wafer is cut by a dicing cutter at the position indicated by the arrow, the AT-cut quartz substrate shown in FIG. 1 is obtained.

FIGS. 4 (a), 4 (b), and 4 (c) show a case where both surfaces of the wafer are half-etched shallow (one surface has an etching depth t '), and a method of manufacturing the AT-cut quartz substrate shown in FIG. FIG. As in the case of FIG. 3, dicing is performed at a lattice-shaped groove indicated by an arrow to separate into individual pieces.

FIG. 5 is a view showing another means for obtaining the AT-cut quartz crystal substrate shown in FIG. 1. The method for etching both surfaces is the same as that shown in FIG. By narrowing the gap, the shape of the etching on the back side becomes an acute angle, it is possible to divide the crystal substrate into individual quartz substrates by applying a knife edge at the arrow without using a dicing cutter and applying a little force. it can.

[0014]

Since the present invention is configured as described above, the first aspect of the present invention exhibits an excellent effect that the resonance frequency of the high-frequency crystal substrate can be measured with high accuracy. The invention according to claim 2 has an excellent effect that the resonance frequency of the high-frequency crystal substrate can be measured with high accuracy, and the yield of the crystal substrate is improved.

[Brief description of the drawings]

1A and 1B are diagrams showing a configuration of a high-frequency crystal substrate according to the present invention, wherein FIG. 1A is a plan view, FIG. 1B is a cross-sectional view in the Z′-axis direction,
(C) is a cross-sectional view in the X-axis direction, and (d) is a frequency spectrum near the resonance frequency.

FIG. 2 is a cross-sectional view in the X-axis direction showing a configuration of another invention.

FIGS. 3A to 3C are cross-sectional views showing steps of forming a quartz substrate having the shape shown in FIG.

4 (a) to 4 (c) are cross-sectional views showing steps of forming a quartz substrate having the shape shown in FIG.

FIGS. 5A and 5B are cross-sectional views showing steps of forming a quartz substrate having the shape shown in FIG.

FIG. 6 is a diagram illustrating the formation of a conventional high-frequency crystal substrate.
(A) is a diagram in which recesses formed by photolithography and etching of a wafer are arranged in a matrix, (b) is a substrate divided into individual pieces, and (c) is a cross-sectional view thereof.

FIG. 7 is a flowchart for forming a high-frequency substrate having a recess.

FIG. 8 is an air gap type apparatus for measuring a resonance frequency of a high frequency quartz substrate.

FIG. 9 is a diagram showing a frequency spectrum of a conventional high-frequency crystal substrate.

[Explanation of symbols]

 L: long side of rectangular quartz substrate L ': short side of rectangular quartz substrate a: polishing width t: polishing thickness t': polishing thickness

Claims (2)

[Claims] 1. A high-frequency quartz substrate in which at least one of four main surfaces of a rectangular AT-cut quartz substrate is half-etched by a predetermined depth, a width a of the half-etched portion and a length of the substrate. The relationship with the side L is 2a / L
A quartz substrate characterized by satisfying ≒ 0.1. 2. A step of forming a protective film having a lattice-shaped exposed portion having a predetermined width on at least one surface of an AT-cut quartz wafer, a step of wet-etching the quartz wafer to a desired depth in the exposed portion, A step of cleaning the substrate and stopping the etching, a step of removing the protective film, and a step of cutting into individual pieces along the etched portion.