JPH04294622A - Production of piezoelectric element - Google Patents

Abstract

PURPOSE:To realize the manufacture implementing stable wafer processing even in the piezoelectric element whose piezoelectric substrate is required to be made thin. CONSTITUTION:A process of etching making the thickness of an exciting part of, at least, a piezoelectric element 11 thinner than the thickness of a frame part 12 in the manufacture of the piezoelectric element manufacturing plural piezoelectric elements 11 from one piezoelectric substrate with the etching processing in the lump, is realized.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing piezoelectric elements such as piezoelectric vibrators and piezoelectric filters using piezoelectric materials such as quartz. In particular, the present invention relates to a method of manufacturing a piezoelectric element in which a plurality of piezoelectric elements are simultaneously formed from a single piezoelectric substrate by photo-etching.

0002

2. Description of the Related Art A method of simultaneously forming a plurality of piezoelectric elements from a single wafer by photo-etching has been highly acclaimed for its high mass productivity.

A conventional manufacturing method will be explained using an example of an AT-cut crystal resonator. The conventional manufacturing process for AT-cut crystal resonators generally includes (1) wafer cutting, (2) wafer polishing, (3) metal film formation, (4) external shape photo-etching, (5) electrode film formation, (6) Vibration piece mount, (
It is divided into 7) frequency adjustment and (8) sealing.

In the wafer cutting process, raw crystal is cut into wafers at a predetermined cut angle. A wire saw is used for cutting. Although the size of the wafer depends on the size of the crystal raw stone, it is approximately 30 mm square, which is a size that allows about 40 to 100 rectangular crystal vibrating pieces to be obtained from one crystal wafer.

In the wafer polishing process, the wafer is polished with an abrasive to a predetermined thickness and required flatness. First, use a polishing agent with large abrasive grains, and gradually move to a polishing agent with finer grains to achieve the desired thickness and flatness.

In the metal film forming step, after cleaning the polished quartz wafer, chromium and gold are formed on the wafer surface by sputtering.

In the external shape photo-etching process, a photosensitive resist is first applied to the wafer surface, and then the external pattern is exposed to light using an exposure machine. After that, the resist film is developed and gold and chromium are etched. Next, the crystal is etched using the gold and chromium film as a corrosion-resistant film. As a result, the external pattern of the crystal vibrating piece exposed to the resist film is formed into the shape of an actual crystal vibrating piece. After crystal etching, the resist film, gold, and chromium film are peeled off.

In the electrode film forming step, metal masks are set on the front and back sides of a crystal wafer on which a plurality of crystal vibrating pieces are formed, and chromium and silver are vapor-deposited. The metal mask has a hole in the electrode formation part, and chrome,
Silver is deposited to form an electrode.

In the vibrating element mounting step, each crystal vibrating element is broken off from the tie bar portion of the crystal wafer on which a plurality of crystal vibrating elements are formed, and is soldered and fixed to the lead of the plug.

In the frequency adjustment step, while measuring the frequency with the two leads of the plug, silver is deposited on the electrode portion of the crystal vibrating piece to adjust it to a predetermined frequency.

In the sealing step, the case is press-fitted into the plug to vacuum seal it. With the above steps, the crystal resonator is completed.

FIG. 2 is a plan view of a crystal wafer in a state where a conventional crystal vibrating piece is formed. Reference numeral 1 indicates a crystal vibrating piece, and a plurality of crystal vibrating pieces are formed in a crystal wafer. 2 is a frame for forming each crystal vibrating piece into a wafer state.

FIG. 3A is an enlarged plan view of a crystal wafer in a state where a conventional crystal vibrating piece is formed. 1 is a crystal vibrating piece, 2
3 is a frame, and 3 is a tie bar connecting the crystal vibrating piece 1 and the frame 2. When mounting the vibrator, tie bar 3
At this point, separate the crystal vibrating piece 1 from the frame 2. 4, 5
are an excitation electrode and a mount electrode formed on the crystal vibrating piece. By soldering the lead of the plug and the mount electrode 5, the crystal vibrating piece 1 is fixedly supported on the plug.

FIG. 3(b) is a cross-sectional view taken along line AA' in FIG. 3(a), and the names of each part are the same as in FIG. 3(a). The thickness of the crystal in each part is uniform.

[0015]

[Problems to be Solved by the Invention] However, in the case of a piezoelectric element using a thickness shear vibration mode, in order to obtain vibration in a high frequency band, it is necessary to make the piezoelectric substrate thinner accordingly. In this case, the above-mentioned conventional technique has the problem that the wafer becomes thin and the wafer breaks during the process due to insufficient mechanical strength. In particular, it is extremely difficult to polish thin piezoelectric substrates with high precision.

The present invention is intended to solve these problems, and its purpose is to provide a manufacturing method that allows stable wafer processing even for piezoelectric elements that require thinner piezoelectric substrates for high frequency bands. It's there.

[0017]

[Means for Solving the Problems] The method of manufacturing a piezoelectric element of the present invention is a method of manufacturing a piezoelectric element in which a plurality of piezoelectric elements are manufactured at once from a single piezoelectric substrate by etching process, in which at least an excitation portion of the piezoelectric element is manufactured. It is characterized by having an etching step so that the thickness is thinner than that of the frame portion.

[0018]

[Embodiment] The process of manufacturing an AT-cut crystal resonator in an embodiment of the present invention is as follows. (1) Wafer cutting, (2) Wafer polishing, (3) Metal film formation, (4) External shape photo-etching, (5) Excitation part metal film removal, (6
) Excitation part crystal half etching, (7) Electrode film formation, (
8) Vibration element mount, (9) frequency adjustment, (10) sealing.

The wafer cutting process is similar to the prior art.

In the wafer polishing process, the wafer is polished to a predetermined thickness and flatness using an abrasive as in the prior art, but it is not necessary to polish the wafer to a thickness that allows the desired frequency to be obtained. This is because in a later process, the crystal in the excitation section that determines the frequency will be half-etched to make it thinner. It can be thicker by 5 microns or more than the conventional one. Therefore,
The wafer polishing process is easier than in the past. This is because if the wafer is thin, even if it is 5 microns, the yield and number of steps will vary considerably.

The metal film forming process is the same as the conventional one.

The external shape photo-etching process is almost the same as the conventional one, but after crystal etching, only the resist film is peeled off, leaving the gold and chromium films.

In the excitation part metal film removal step, a photosensitive resist is again applied to the wafer surface, and this time the shape of the excitation part is exposed to light using an exposure machine. In FIG. 3A, the excitation section is the portion of the crystal vibrating piece 1 excluding the mount electrode portion. Next, the resist is removed to remove the resist in the excitation area, and further, the gold and chromium films in the excitation area are removed. At this time, the gold and chrome films remain on the frame.

In the excitation section crystal half-etching step, the excitation section crystal is etched using a gold or chromium film as a corrosion-resistant film. The etching solution used is hydrofluoric acid or a mixture of hydrofluoric acid and ammonium fluoride. At this time, since the rate of crystal etching by the etching solution is known in advance, time management is performed so that a predetermined thickness remains as the excitation part of the crystal vibrating piece. After immersing in etching solution for a specified period of time, cleaning
The resist film, gold, and chromium film formed on areas other than the excitation part are peeled off.

The electrode film forming process, vibrating element mounting process, frequency adjustment process, and sealing process are the same as those of the conventional technique.

FIG. 1(a) is an enlarged plan view of a crystal wafer in a state where an AT-cut crystal vibrating piece is formed using a manufacturing method according to an embodiment of the present invention. In FIG. 1A, 11 is a crystal vibrating piece, 12 is a frame, 13 is a tie bar, 14 is an excitation electrode, and 15 is a mount electrode.

FIG. 1(b) is a cross-sectional view taken along line BB in FIG. 1(a), and the symbols and names of each part are the same as in FIG. 1(a). In FIGS. 1(a) and 1(b), the functions of each part are the same as in the conventional technology.

In FIG. 1(b), the part of the crystal vibrating piece 11 where the mount electrode 15 is formed and which is thinner than the thickness of the crystal vibrating piece is the excitation part, and the excitation electrode 14
A piezoelectric effect is generated by applying a voltage to and applying an electric field to the crystal of the crystal resonator excitation section. By connecting the oscillation circuit through the mount electrode 15, thickness shear vibration is generated in the excitation section, resulting in stable vibration. Thickness shear vibration is
It is almost determined by the thickness of the crystal in the excitation part, and the thinner the crystal, the higher the frequency vibration.

The thickness of the crystal vibrating piece in the frame 12, tie bar 13, and mount electrode 15 portion is thicker than the thickness of the excitation part of the crystal vibrating piece 11, so that even if the wafer is handled in the process after etching the external shape of the crystal vibrating piece, the wafer It has mechanical strength that prevents it from cracking.

In FIGS. 1A and 1B, only the excitation section is half-etched, but the entire crystal vibrating piece 11 including the mount electrode 15 may be half-etched. Further, the tie bar 13 portion may also be included.

In the above embodiment, the cantilevered rectangular shape A
Although the method for manufacturing a T-cut crystal resonator has been described, it may be supported on both sides or in a disk shape. Furthermore, instead of a crystal resonator, a piezoelectric element using a crystal filter or other piezoelectric material (lithium tantalate, etc.) may be used.

Further, in the embodiment, wet etching using an etching solution was used, but the same effect can be obtained by using dry etching, or a piezoelectric material thinning technique using ion beam sputtering, excimer laser, or the like.

[0033]

As described above, according to the present invention, there is a step of etching so that at least the excitation part of the piezoelectric element is thinner than the frame part, so there is no need to make the piezoelectric substrate particularly thin. When manufacturing a piezoelectric element using a certain thickness-shear vibration mode, the extremely difficult process of polishing a thin plate was made easier, and the improved wafer strength reduced wafer breakage during other processes related to wafer processing. Therefore, an overall improvement in retention was achieved.

Furthermore, it has now become possible to process a high-frequency piezoelectric element, such as a 50 MHz fundamental wave AT-cut crystal resonator, and a wafer with a crystal plate thickness of about 30 μm, which has been impossible until now.

The present invention realizes a piezoelectric element with a wider frequency range while ensuring mass productivity in wafer processing, and has great effects.

[Brief explanation of drawings]

FIG. 1: AT using the manufacturing method in the embodiment of the present invention
FIG. 3 is an enlarged view showing a crystal wafer in a state where cut crystal vibrating pieces are formed, in which (a) is a plan view and (b) is a cross-sectional view taken along line BB in (a).

FIG. 2 is a plan view of a crystal wafer in a state where a conventional crystal vibrating piece is formed.

FIG. 3 is an enlarged view of a crystal wafer in a state where a conventional crystal vibrating piece is formed, in which (a) is a plan view and (b) is a cross-sectional view taken along line A-A in (a).

[Explanation of symbols]

1, 11 Crystal vibrating piece 2, 12 frame 3, 13 Tie bar 4, 14 Excitation electrode 5, 15 Mount electrode

Claims (1)

[Claims] Claims: 1. A method for manufacturing a piezoelectric element in which a plurality of piezoelectric elements are manufactured at once from a single piezoelectric substrate by etching, comprising the step of etching so that at least the excitation part of the piezoelectric element is thinner than the frame part. A method of manufacturing a piezoelectric element, characterized by: