JP2004018291A - Process for manufacturing quartz thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a process for manufacturing a quartz thin film showing a high crystallinity using inexpensive water glass. <P>SOLUTION: A crystal plate is prepared as a substrate, and an aqueous solution essentially comprising water glass is applied onto the surface of the substrate, exposed to UV and baked to form the quartz thin film. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a crystal thin film for use in a crystal resonator, a crystal filter, or the like.
[0002]
[Prior art]
Crystal oscillators are used as important devices indispensable for information communication due to their high stability. In recent years, with the development of communication satellites, mobile phones, and the like, high frequency and miniaturization thereof are one of the major goals.
[0003]
Conventionally, a quartz oscillator is cut out of a thin plate from a large crystal synthesized by hydrothermal synthesis using a mechanical processing means such as a multi-blade saw, and polished using the same mechanical processing means to obtain the required thickness. It was manufactured by the method of finishing. However, this method is uneconomical because it requires a large-scale apparatus such as an autoclave and also cuts and discards a large part of the synthesized crystal during processing. Further, it is difficult to process the vibrator to a thickness of several tens μm or less by a mechanical processing means, and thus it is difficult to manufacture a small and high-frequency vibrator.
[0004]
In order to solve these problems, Japanese Patent Application Laid-Open No. 8-157297 proposes a method for producing a single crystal thin-film crystal by a sol-gel method, and Japanese Patent Application Laid-Open No. 5-327383 proposes a method for processing a quartz crystal plate. The sol-gel method does not require a high-pressure autoclave or the like, but requires many complicated processes such as addition of alcohol, water, and amine to a raw material solution, reflux, coating on a substrate, drying, and heat treatment.
On the other hand, the inventors of the present invention have developed an atmospheric-pressure atmospheric pressure gas that is epitaxially grown on a substrate by reacting a silicon alkoxide raw material with oxygen under atmospheric pressure without using a vacuum device in order to produce a crystal thin film by a simpler method. A phase epitaxy growth method (AP-VPE) is proposed in Japanese Patent Application No. 2000-270,300.
[0005]
[Problems to be solved by the invention]
However, the atmospheric pressure vapor phase epitaxy (AP-VPE) has a problem that carbon of ethyl silicate used as a raw material is likely to be mixed as an impurity. Further, although the quartz thin film formed by the atmospheric pressure vapor phase epitaxy (AP-VPE) does not contain sodium, a quartz containing a small amount of sodium has better oscillation characteristics when a quartz oscillator is used. (Natural quartz and crystals produced by hydrothermal synthesis contain sodium).
[0006]
An object of the present invention is to provide a manufacturing method in which sodium is contained in a manufactured quartz thin film by means similar to or easier than the above-mentioned atmospheric pressure vapor phase epitaxy (AP-VPE). It is in.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a method for manufacturing a quartz crystal thin film according to claim 1 according to the present invention comprises:
Preparing a crystal plate as a base material,
Applying an aqueous solution containing water glass as a main component on the surface of the base material,
Irradiating the applied aqueous solution with ultraviolet light,
Baking the applied aqueous solution;
Includes
[0008]
According to a second aspect of the present invention, there is provided the production method according to the first aspect, wherein the water glass (sodium silicate) concentration of the aqueous solution containing the water glass as a main component is 0.1 mol / liter to 0.1 mol / l. It is characterized by being between 01 mol / l.
[0009]
Furthermore, the manufacturing method according to claim 3 of the present invention is characterized in that, in the manufacturing method according to claim 1, the pH of the aqueous solution containing water glass as a main component is adjusted to be between 6 and 8. Features.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a method for manufacturing a crystal thin film according to the present invention will be described with reference to the drawings and the like.
[0011]
As shown in FIG. 1, ion-exchanged water is added to the sodium silicate solution to a concentration of 0.0855 mol / liter. Further, a cation exchange resin is added thereto, and the mixture is stirred until pH = 7.7. This becomes the raw material solution.
[0012]
The Si (111) substrate whose surface has been cleaned is fixed on a spin coat table, and irradiated with a 100 W infrared lamp at 70 V for 2 minutes from a distance of 5 cm. Next, after the raw material solution is dropped on the Si substrate, spin coating is performed by rotating the spin coater at 1500 rpm for 2 minutes. At this time, the infrared ray remains irradiated.
[0013]
Subsequently, the Si substrate is irradiated with ultraviolet rays from a distance of 11 cm using a 100 W mercury lamp.
[0014]
Further, the spin-coated Si substrate is fired at 700 ° C. in an electric furnace under a supply of oxygen of 25 sccm.
[0015]
As described above, a quartz thin film is formed on the Si substrate.
[0016]
At this time, the concentration of sodium silicate and the pH of the raw material solution are important for the formation of a thin film. That is, unless the concentration of sodium silicate is between 0.1 mol / l and 0.01 mol / l, the film does not form. In particular, a film near 0.0855 mol / liter is best. Further, if the pH of the aqueous solution of sodium silicate is not less than 6 and not more than 8, the film is not formed, and the film is most preferably formed around 6.8 to 7.7.
[0017]
The formed thin film was evaluated as follows. For the evaluation, a scanning electron microscope (SEM), an atomic force microscope (AFM), an X-ray photoelectron spectroscopy (XPS), and a two-crystal X-ray diffraction (DC-XRD) were used.
[0018]
FIG. 2 is a diagram illustrating a crystal thin film manufactured by the method of the present invention, which is measured using a two-crystal X-ray diffraction method (DC-XRD). The measurement device was RAD-IIB manufactured by Rigaku Denki, and the measurement was performed under the conditions of an X-ray tube applied voltage of 25 kV and a current of 20 mA.
[0019]
As apparent from FIG. 2, analytical peaks were confirmed at 28.4 °, 27.7 °, and 26.7 °. Of these, 28.4 ° is the peak of the Si substrate (111 plane). The peak at 26.7 ° corresponds to the (101 face) of α-crystal. 27.7 ° is considered to be Na ₂ Si ₂₀ O ₄₁ · xH ₂ O, Na ₂₀ · 39SiO _2, or the like.
[0020]
When each of the thin films formed by changing the ultraviolet irradiation time from 0 minute to 60 minutes is measured, as the ultraviolet irradiation time becomes longer, the diffraction peak of the α-crystal (101) plane increases and the peak at 27.7 ° decreases. . In other words, irradiating with ultraviolet rays promotes crystallization into α-quartz.
[0021]
In addition, two-crystal X-ray analysis (DC-XRD) measurement was performed by rotating a material having a firing temperature of 700 ° C. and an ultraviolet irradiation time of 60 minutes from −5 ° to + 5 ° in the ω direction with respect to the α-crystal (101) plane. As a result, as shown in FIG. 3, it was found that the surface of the α crystal (101) was oriented at + 3 ° and −3 ° with respect to the Si substrate (111).
[0022]
The crystal of the crystal can be represented as shown in FIG. 4A when only silicon atoms are taken out, but can be represented as shown in FIG. 4B when viewed from the arrow A in FIG. Here, the plane passing through (1) and (2) is + 3.32 ° with respect to the (101) plane, and the plane passing through (1) and (3) is also -2.89 ° with respect to the (101) plane. The three peaks observed in 3 are considered to be the planes passing through the silicon atoms (1)-(2), (1)-(3), and (1)-(4) in FIG.
[0023]
Since (101) of the α crystal generated in the present invention has a lattice constant of a = 4.913 [Å] and c = 5.405 [Å], it is 38.2 ° with respect to the Z axis. In contrast, AT cuts often used in industrial applications are inclined at 35.25 ° with respect to the Z axis. Therefore, by selectively growing the crystal thin film having the inclination of (1)-(3), a crystal thin film having a crystal angle very close to the AT cut can be efficiently manufactured.
[0024]
Then, it is an example of the result measured by X-ray photoelectron spectroscopy (XPS) for the surface element analysis of the quartz crystal thin film produced | generated by this invention. XRATOS-XSM800Vpci manufactured by Shimadzu Corporation was used as a measuring instrument. As an X-ray source, Mg3.6 radiation of 1253.6 eV was used, and the acceleration voltage was 12 kV and the current was 20 mA. In the measurement, the thin film surface was etched with Ar for 2 minutes.
[0025]
As a result, Si, O 2 and Na were observed as shown in FIG. In this analysis, there was no significant difference between the thin films subjected to UV irradiation for 0, 20, 40, and 60 minutes, respectively. Since the area ratio O1s / Si2p of the peaks of O1s and Si2P is 1.17, which is almost the same as 1.15 of quartz glass or 1.12 of quartz crystal, it was confirmed that the resulting thin film was SiO _2. Was.
[0026]
Further, in order to examine the film thickness of the quartz thin film formed in the present invention, observation was performed with a scanning electron microscope (SEM). The apparatus used was observed under the conditions of SUPERSCAN-220 manufactured by Shimadzu Corporation, an electron beam acceleration voltage of 15 kV, a spot size of 3, and a working distance of 5.
[0027]
A comparison was made between the materials produced at firing temperatures of 500 ° C. and 700 ° C. and ultraviolet irradiation times of 0, 20, 40, and 60 minutes. Was. FIG. 6 shows a representative SEM image. It was confirmed that the film thickness depends on the conditions such as the concentration of the raw material solution during spin coating and the number of rotations. It was found that the interface between the quartz thin film and the Si (111) substrate was steep and the surface was uniform.
[0028]
Subsequently, an atomic force microscope (AFM) observation was performed to clarify the surface morphology of the generated quartz thin film. The AFM used was SPM-9500 manufactured by Shimadzu Corporation under the conditions of a scanning range of 30 μm and a scanning height of 800 nm.
[0029]
FIG. 7 shows an example of measuring a material at a firing temperature of 700 ° C. and an ultraviolet irradiation time of 60 minutes. It can be seen that the mean square roughness (RMS) is 140 nm and is composed of an aggregate of hexagonal plate-like crystals inclined about 3 °. Since this inclination coincides with the angle appearing in the XRD pattern rotated in the ω direction, it was confirmed that the α crystal (101) plane had a constant inclination and was grown on the Si (111) plane.
[0030]
【The invention's effect】
As described above, the quartz crystal thin film can be produced from an inexpensive water glass solution by a simple method such as spin coating and baking, so that the manufacturing process of a quartz crystal thin film which has been complicated so far can be easily performed. In addition to this, the quartz thin film according to the method of the present invention contains a trace amount of sodium, which is said to provide good oscillation characteristics when applied to a quartz oscillator. Since the thickness of the crystal thin film can be controlled under other conditions, and it is easy to make the film very thin, it is easy to manufacture a crystal resonator having a resonance frequency of 100 MHz or more, which has been difficult to obtain.
[Brief description of the drawings]
FIG. 1 is a view showing an embodiment of a method for manufacturing a quartz crystal thin film according to the present invention.
FIG. 2 is a view showing an XRD pattern of a crystal thin film generated in the embodiment of FIG.
FIG. 3 is a view showing an XRD pattern obtained by rotating the crystal thin film generated in the embodiment of FIG. 1 from −5 ° to + 5 ° in the ω direction with respect to the α-crystal (101) plane.
FIG. 4A is a diagram showing a quartz crystal (101) plane only with silicon atoms.
FIG. 4B is a view as seen from arrow A in FIG. 4A.
FIG. 5 is a diagram showing an elemental analysis of the quartz thin film formed in the embodiment of FIG. 1 by XPS.
6 is a photograph of an image obtained by observing a cross section of the quartz thin film formed in the example of FIG. 1 by SEM.
7 is a photograph of an AFM image of the quartz crystal thin film generated in the example of FIG.

Claims (3)

Preparing a crystal plate as a base material,
Applying an aqueous solution containing water glass as a main component on the surface of the base material,
Irradiating the applied aqueous solution with ultraviolet light,
Baking the applied aqueous solution;
A method for producing a quartz thin film including: A method for producing a quartz crystal thin film, wherein the aqueous solution containing water glass as a main component has a water glass ({sodium silicate)} concentration of 0.1 mol / l to 0.01 mol / l. A method for producing a quartz crystal thin film, wherein the aqueous solution containing water glass as a main component is prepared so as to have a pH of 6 to 8.

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