JPS6294007A - Manufacture of piezoelectric thin film resonator - Google Patents

Abstract

PURPOSE:To form a recess with excellent accuracy in size without side face etching by applying the etching while the etching liquid formed by mixing an organic film forming agent is allowed to collide against the main surface. CONSTITUTION:An Si oxide film 10, a lower electrode 12, a zinc oxide made piezoelectric thin film 14, an upper electrode 15 and a protection film 16 are formed sequentially on the one main surface 11a of a zinc oxide sintered substance made supporting substrate 11. Then a mask 17 is formed on the other main surface 11b and the etching is applied while the etching liquid A0 formed by mixing the organic film forming agent is allowed to collide against the main surface 11b. Since the etching is applied while the organic film 22 of the organic film forming agent is formed to the inner wall of the recess 18, the etching to the side wall of the recess 18 is suppressed to form the recess 18 with high dimensional accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a piezoelectric thin film resonator that can be used in the Vi-(F and UHF frequency bands).

(Prior art) In general, so-called bulk wave resonators, which utilize the basic thickness vibration of a piezoelectric substrate such as ceramic or quartz, have a limited thickness due to limitations in processing technology and mechanical strength of the piezoelectric substrate. The limit is several 10 μm, and therefore the usable resonance frequency is also limited to several tens of MHz.

Therefore, in recent years, a so-called diaphragm type pressure N has been developed, which can utilize semiconductor manufacturing technology as is and has the configuration shown in Figures 5 and 6, which operates in the VHF and LJ HF ultra-high frequency bands. ! V-film resonators have been studied (for example, JP-A-60-68706, JP-A-60-687IO, and JP-A-60-687).
(See Publication No. 68711).

The piezoelectric thin film resonator has a silicon oxide thin film 2 formed on one main surface of a silicon single crystal support substrate l, a first electrode 3, a piezoelectric thin film 4 of zinc oxide, and a second electrode 3 on the silicon oxide thin film 2. While sequentially forming the electrodes 5, the silicon single crystal supporting substrate l is anisotropically etched into a diaphragm shape from the other main surface of the silicon crystal supporting substrate l toward the piezoelectric thin film 4, and the piezoelectric thin A recess 6 is formed to enable thickness vibration of @4.

By the way, the formation of the recess 6 by the above-mentioned anisotropic etching of the Noricon single crystal support substrate l utilizes the difference in etching speed between the (100) plane and the (111) plane of the Noricon single crystal support substrate l, and the etching The problem was that it was difficult to control. Furthermore, since the above-mentioned pressure-N thin film resonator uses a silicon single crystal substrate I, there is also a problem that the cost is high. On the other hand, it is also possible to use an inexpensive polycrystalline substrate instead of the silicon single crystal substrate 1;
When forming the recess 6 by etching, the inner wall of the recess 6 is also etched, resulting in so-called side surface etching, making it difficult to form the recess 6 with good dimensional accuracy.

(Object of the Invention) An object of the present invention is to manufacture a piezoelectric thin film resonator in which a concave portion with good dimensional accuracy and no side etching is formed in a supporting substrate of the piezoelectric thin film resonator made of a sintered body containing zinc oxide. The purpose is to provide a method.

(Structure of the Invention) Therefore, the present invention uses an organic thin film forming agent when forming a recess under the vibration region of the piezoelectric thin film by etching on the support substrate of the piezoelectric thin film resonator made of a sintered body containing zinc oxide. The method is characterized in that the mixed etching solution is made to collide with the substrate, and the supporting substrate is etched in seven directions while depositing an organic film on the inner wall. That is, in the present invention, an organic film is deposited on the inner walls of the four parts formed on the support substrate during etching, and this organic film suppresses etching of the inner walls of the recessed portion, and etches the support substrate in the thickness direction thereof. It is something.

(Effects of the Invention) According to the present invention, etching of the inner wall of the recess formed by etching on the support substrate is suppressed by the organic film deposited during etching, so that the sintering of polycrystalline zinc oxide is prevented. It is also possible to form recesses with good dimensional accuracy in the supporting substrate made of a solid body. Further, according to the present invention, since a support substrate made of polycrystalline zinc oxide can be used, the cost of the piezoelectric thin film resonator can also be reduced.

(Example) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

First, MnC0* and VtOs are added to zinc oxide (ZnO), and wet-mixed so that manganese (Mn) and vanadium (V) are contained at 5 at % and 0.1 at %, respectively. After pulverizing this with a wet mill, it is press-formed into a flat plate shape and sintered at about 1200°C for 2 hours. The resulting sintered body (not shown) with a thickness of 10 mm and a size of 50 x 50 mm was cut into slices with a thickness of 0.5 mm.
Mirror polishing is performed using #8000 SiC to create a flat supporting substrate 2 having a thickness of 0.3 mm as shown in FIG. 1(a). As described above, the reason why manganese is added to zinc oxide is to increase the insulation resistance of the support substrate 11, and the support substrate 11 has an insulation resistance of 1010 ohms or more. Further, the reason why vanadium is added to zinc oxide is to improve the sinterability of zinc oxide and obtain a sintered body with high density.

As shown in FIG. 1(b), a silicon oxide film 10 with a thickness of approximately 6000 angstroms is deposited on the major surface 11a of the support substrate 11 prepared as described above by r(F magnetron sputtering). Form into a thick layer.

Next, on this silicon oxide film IO, as shown in FIG. Formed by sputtering method. When forming the lower electrode 12 by this sputtering method, the silicon oxide film 0 is an oxide, and the lower electrode 12 to be formed is
Since it is easily oxidized, it is preferable to carry out the process in a mixed gas of Ar:Ht-80:20. Note that this silicon oxide film 10 is, as will be described later, a supporting substrate! Functions as a stop layer for etching No. 1.

Next, as shown in FIG. 1(d), the lower electrode 1
A piezoelectric thin film 14 made of a C-shaped zinc oxide crystal is formed on the silicon oxide film 10 by RF magnetron sputtering.

On the piezoelectric thin film 14, as shown in FIG. 1(e), an upper electrode 1 having the same constant elastic steel composition as the lower electrode 12 is placed.
5 is formed by a sputtering method.

Thereafter, in order to prevent the piezoelectric thin film 14 made of zinc oxide from absorbing moisture and deteriorating its characteristics, a photosensitive film was applied from above the piezoelectric thin film 14 and the upper electrode 15 as shown in FIG. A protective film 16 is formed by spin-coating polyimide and exposing it to ultraviolet light. This protective film 16 has a small mass so that the thickness vibration of the piezoelectric thin film 14 is not inhibited.
In addition, it is preferable that the thickness is thin.

The thickness t of the piezoelectric thin film 14 is determined by t=N/f, where the target resonance frequency is r (Hz) and the frequency constant specific to the composite diaphragm is N (I-1z, mm). be done.

Through the above steps, one main surface 11a of the support substrate 11
On top, a silicon oxide film 10, a lower electrode 12, a piezoelectric thin film 1
4. After forming the upper electrode 15 and the protective film I6, from the other main surface 1tb of the support substrate 11 toward the vibration region 21 of the piezoelectric thin film 14 that is sandwiched between the lower electrode 12 and the upper electrode 15 and performs thickness vibration. , the recess 18 (see FIG. 1(f)) is formed by the method that characterizes the present invention.

That is, as shown in FIG.
A mask 17 is formed by exposure to ultraviolet light. This mask 1
Since the photosensitive polyimide constituting the substrate 7 is sensitive to alkali, the supporting substrate 11 is etched with an acid.

Therefore, an etching solution is prepared by dispersing organic film forming agents such as diethylbenzene, sodium sulfonate, oleic acid, and highly sulfated oil in an acidic etching solution such as hydrochloric acid or nitric acid using a surfactant.

The etching solution is applied to the other main surface 11b of the support substrate 11 through the mask 17, as shown by the arrow Ao in FIG. , etching the support substrate II. During this etching process, the organic film forming agent dispersed in the etching solution is deposited as an organic film 22 on the inner wall of the recess 18 formed in the supporting substrate 11.

The organic film 22 is formed in a recess I formed on the support substrate 11.
The inner wall of I8 is sealed against the etching solution to prevent the side wall of I8 from being etched. As a result, the support substrate 11 has a concave portion I without side etching.
8 is formed. In this example, etching stopped at the silicon oxide film IO, and in the case of the support substrate 11 having a thickness of 0.3 mm, etching of the four parts 18 was completed in about 30 minutes.

Note that during etching of the support substrate 11, in order to maintain uniformity of etching, the support substrate 11 is rotated and
It is preferable to control the temperature of the etching solution to be constant.

Further, the formation of the four parts 18 by this etching includes the lower electrode 12, the piezoelectric thin film 14, and the upper electrode 1 on the supporting substrate 11.
5, after the step in FIG. 1(b), and then in the steps in FIG. 1(C) to FIG. 1(e),
A lower electrode 12, a piezoelectric thin film 14, etc. may be formed.

After forming the recess 18 in the supporting substrate 11 by etching as described above, in order to prevent the substrate 1.1 made of zinc oxide from absorbing moisture, the recess 18 is etched as shown in FIG. 1(h). A protective film 20 is formed from the inner wall surface of the support substrate 18 to the other main surface llb of the support substrate 11. This protective film 2
0 can use the same photosensitive polyimide as the protective film 16.

Through the above steps, a diaphragm-shaped piezoelectric thin film resonator using a sintered body of zinc oxide can be obtained.

In the above embodiments, as the etching solution, in addition to nitric acid, acids such as hydrochloric acid (HcQ) and sulfuric acid (H, So, ) can also be used.

In the above embodiments, an acidic etching solution was used, but since zinc oxide can be etched with either acid or alkali, an alkaline etching solution can also be used.

Next, an example in which an alkaline etching solution is used will be described.

When using an alkaline etching solution, as shown in FIG. 1(b), the silicon oxide film lO is not formed on one main surface 11a of the support substrate 11, and the main surface 11a of the support substrate ti is removed. A lower electrode 12 made of an alkaline earth metal material is directly formed in the opening, and this lower electrode 1
2 is used as an etching stop layer for the supporting substrate 11.

The following steps are substantially the same as those described in FIGS. 1(a) to 1(h), except that the supporting substrate 11
The following etching solution is used to form the recess 18.

Diethylbenzene 4 in sodium hydroxide with a concentration of 30%
%, isopropylnaphthalene 0.01%, and sodium sulfonate 0.01% are dispersed and balanced using a surfactant.

According to the above embodiment, the etching depth is d.

The corrosion coefficient defined by F=2d/V can be set to 50 or more, where the line width reduction is V, and as shown in FIG. , almost no side etching occurs.

On the other hand, as shown in FIG. 3 and FIG. When the support substrate 11 was etched with an etching solution, side surface etching occurred and the corrosion coefficient was about 1.6.

[Brief explanation of drawings]

Figure 1(a), Figure 1(b), Figure 1(c), Figure 1(
d), FIG. 1(e), FIG. 1(f), FIG. 1(g), and FIG. 1(h) are explanatory diagrams of the method for manufacturing a piezoelectric thin film resonator according to the present invention, and FIG. , FIG. 3 and FIG. 4 are explanatory diagrams of the side surface etching that occurs on the supporting substrate during the production of piezoelectric thin film resonators by the method of the present invention and the conventional method, respectively, and FIG. Perspective view,
FIG. 6 is a sectional view taken along line A--A in FIG. 5. 10... Silicon oxide film, 11... Support substrate,
11a, llb... Main surface, 12... Lower electrode, 14... Piezoelectric thin film, I5... Upper electrode, 18
... recess, 21 ... vibration region, 22 ... organic film. Patent applicant Murata Manufacturing Co., Ltd. Agent Patent attorney Aoyama Aoyama and two others. Night b 11b b Q fa

Claims (1)

[Claims] (1) The vibration region of the piezoelectric thin film formed on one main surface of a support substrate made of a sintered body containing zinc oxide was formed toward the vibration region from the other main surface of the support substrate. A method for manufacturing a piezoelectric thin film resonator supported so as to vibrate on a recess, the method comprising: impinging the other main surface of the substrate on the recess with an etching solution mixed with an organic film forming agent;
A method of manufacturing a piezoelectric thin film resonator, which comprises etching a supporting substrate in its thickness direction while depositing an organic film on the inner wall.