JP3528282B2 - Manufacturing method of single crystal thin film quartz - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal thin film crystal used for an oscillator, a vibrator, a surface acoustic wave device for a high frequency filter, an optical waveguide, etc., and a method for manufacturing the same.

[0002]

Quartz is a low temperature phase of silicon dioxide (<573
However, the skeleton of the quartz mold which is the basis of this quartz crystal structure is not stable unless it is 870 ° C. or lower. However, the melting point of silicon dioxide is much higher than this, 1730 ° C.
Since the cristobalite crystal structure is stable in the vicinity of this melting point, it is said that quartz cannot be synthesized by a simple high temperature treatment.

As a conventional crystal manufacturing technique, there has been only a hydrothermal synthesis method in which a crystal single crystal is grown on a seed crystal from an alkaline solution of silicon dioxide by providing a temperature difference under high temperature and high pressure. The manufacturing process of the crystal by this method is, for example, Ceramics 15 (1980), No. 3, p.
5 are described.

According to the above-mentioned document, the method for producing quartz by the hydrothermal temperature difference method is to fill a large autoclave with an alkaline aqueous solution (for example, 0.5 to 1N NaOH or Na ₂ CO ₃ aqueous solution) and to lower the container. A raw quartz crystal (lasker) and a seed crystal are placed in the upper part of the container through a convection control plate, and the sealed container is heated by an external heater. At that time, the upper part of the container is 330 to 340 ° C. and the lower part is 360 to 370.
℃ to give a certain temperature difference, the internal pressure 800 ~ 15
When a high pressure of 00 kg / cm ² is used, the raw material waste quartz is melted and transported to the upper portion by convection, and becomes supersaturated in the upper portion, which is lower in temperature than the lower portion, and the quartz is deposited and grows on the seed crystal.

This hydrothermal synthesis method can synthesize only large lumpy crystals or granular powders. Therefore, when a thin film is required for use in vibrators, oscillators, surface acoustic wave devices for high frequency filters, etc., this water is used. At present, the large-sized single crystal produced by the thermal synthesis method is cut into a thin film and used.

However, with the recent increase in communication frequency, it is necessary to further reduce the thickness of the crystal. For example, as shown in JP-A-5-327383, the crystal is attached to a semiconductor substrate and polished to form the crystal. A technique for processing a thin film into a thin film has been proposed. However, the thin film manufacturing by processing has a problem that the film thickness that can be processed is limited and the cost becomes high.

[0007]

The hydrothermal temperature difference method, which is a conventional method for manufacturing quartz, requires a large-scale device such as an autoclave for realizing a high pressure, and a large-sized single crystal can be produced by a huge device. Without raising it, the cost cannot be reduced. Further, since it is difficult to form a quartz single crystal having an arbitrary shape by this method, it is necessary to process a large-sized single crystal to cut out a quartz having a desired shape.

In particular, in the case of oscillators, vibrators, surface acoustic wave devices and the like, which are the main applications of quartz, it is necessary to make the quartz thinner as the communication frequency becomes higher in recent years. On the other hand, in the conventional method of cutting a thin crystal from a large single crystal, the thinness of the obtained crystal is practically limited to 50 μm, and it has not been possible to meet the demand for thinning.

In view of the above conventional circumstances, the present invention provides a single crystal thin film crystal having a thickness that can sufficiently meet the recent demand for thinning, and a large-scale apparatus such as an autoclave for the single crystal thin film crystal. It is an object of the present invention to provide a low-cost manufacturing method without the need.

[0010]

In order to achieve the above object, a single crystal thin film quartz crystal provided by the present invention is formed on a single crystal substrate by a sol-gel method and then peeled off from the substrate. It is a single crystal thin film crystal having silicon dioxide of 50 μm or less as a main component.

In the method for producing a single crystal thin film crystal of the present invention, an oxide single crystal film having a crystal type crystal structure containing germanium dioxide as a main component is formed on a single crystal substrate by a sol-gel method. Forming a single crystal thin film crystal containing silicon dioxide as a main component on the single crystal film by a sol-gel method, and then peeling the single crystal thin film crystal from the single crystal substrate by dissolving the oxide single crystal film in an aqueous solution. Is characterized by.

[0012]

The present inventors applied a precursor solution obtained by diluting a silicon alkoxide or the like as a raw material on a single crystal substrate and then heating it to crystallize it by a sol-gel method to obtain an arbitrary size of 5 nm or more. We have found a method of synthesizing a single crystal thin film crystal with a thickness of.

Further, after forming an oxide single crystal film containing germanium dioxide as a main component, a single crystal thin film crystal containing silicon dioxide as a main component is formed, and thereafter germanium dioxide is dissolved in an aqueous solution, particularly an acid or an alkali. It was found that it is possible to manufacture a single crystal thin film crystal by dissolving a single crystal film of germanium dioxide and peeling the single crystal thin film crystal containing silicon dioxide as a main component from the single crystal substrate by taking advantage of the ease. .

Production of a single crystal thin film crystal by the sol-gel method used in the method of the present invention is carried out by the following procedure. First, a single crystal used for the substrate is prepared. This single crystal needs to be a crystal or a single crystal of germanium dioxide having a crystal type crystal structure that can easily grow. It is most preferable to use a single crystal, but use an oxide single crystal such as sapphire or MgO. You can also

Second, a germanium compound soluble in a solvent such as germanium alkoxide is diluted with a solvent such as alcohol, and the obtained metal-containing solution is added with L if necessary.
i, water, amine, etc. are added and the solution is refluxed to form a precursor solution for the sol-gel method. This precursor solution is applied onto a single crystal substrate such as quartz or sapphire by spin coating or dip coating.

The substrate coated with the precursor solution is heated to
The solvent and the like are evaporated to cause gelation and solidification, and further crystallized. This enables low-temperature synthesis of a germanium dioxide oxide single crystal film. In addition, since the coating is performed in the form of a solution, the shape is high and it is easy to form a thin film.

The film thickness of the germanium dioxide oxide single crystal film is adjusted by coating conditions such as the viscosity of the precursor solution, the number of rotations of the substrate, or the pulling rate, and the film is crystallized from the coating until the required thickness is obtained. Repeat until the change.

Thirdly, a silicon compound such as silicon alkoxide is used to prepare a precursor solution for the sol-gel method in the same manner as in the case of germanium dioxide, and the precursor solution is applied onto the germanium dioxide oxide single crystal film. And crystallize to form a single crystal thin film crystal. Here again, in order to adjust the thickness, the coating conditions are adjusted, and coating to crystallization are repeated as many times as necessary.

Finally, the germanium dioxide oxide single crystal film is dissolved in an aqueous solution to separate the single crystal thin film crystal from the substrate. The aqueous solution may be pure water, but is preferably diluted with hydrochloric acid, aqua regia, sodium hydroxide, potassium hydroxide or the like to an appropriate concentration. If necessary, a support plate is attached onto the single crystal thin film crystal, and then the oxide single crystal film is dissolved. A Si wafer or a glass plate having a normal surface and a smooth surface is suitable for the support plate, and it can be firmly bonded by simply pressing it on a single crystal thin film crystal layer and heating it.

The single crystal thin film quartz and the germanium dioxide oxide single crystal film require a thickness of 5 nm or more to form a film having a uniform and stable characteristic due to the problem of smoothness of the coated surface. Further, these thick films can be controlled by adjusting the coating conditions and repeating the coating and drying processes a plurality of times. However, the crystallinity may deteriorate due to stacking of defects, thermal stress, surface roughness, etc., which occur during repetition of each process. Therefore, in order to obtain stable characteristics, the film thickness should be 50 μm or less. preferable.

The heat treatment of the substrate coated with the precursor solution of silicon dioxide or germanium dioxide must be carried out at the temperature required for crystallization. If the heat treatment temperature is lower than 500 ° C., crystallization does not occur, and if it is 1200 ° C. or higher, another kind of crystal structure of a high temperature phase is formed. Therefore, these heat treatment temperatures are preferably in the range of 500 to 1200 ° C. Further, this heat treatment is preferably performed in an oxygen atmosphere or in an atmosphere containing oxygen such as air.

The metal compounds used as raw materials for the sol-gel method include Si (OCH ₃ ) ₄ and Si (OC
₂ H ₅ ) ₄ , Si (OC ₃ H ₇ ) ₄ , Ge (OCH ₃ ) ₄ , Ge
Examples thereof include metal alkoxides such as (OC ₂ H ₅ ) ₄ and Ge (OC ₃ H ₇ ) ₄ , metal acetyl acetates such as Si (COCH ₂ COCH ₃ ) ₄ and metal chlorides such as SiCl ₄ .

Since the piezoelectricity and optical characteristics of an oxide single crystal having a crystal type crystal structure are caused by the crystal structure, all axes of the crystal should be aligned in order to sufficiently exhibit these characteristics. It is necessary to produce a single crystal having excellent crystallinity. By using a single crystal substrate as a substrate and utilizing epitaxial growth in which the crystal structure of the substrate is reflected in the crystal structure of the thin film through bonding at the interface between the substrate and the thin film, a single crystal thin film having excellent crystallinity can be manufactured.

Therefore, in the present invention, by using a single crystal substrate as the substrate, it is possible to produce a single crystal thin film having all crystal axes aligned in the same direction and having excellent crystallinity, and thus excellent characteristics. it can. An oxide single crystal is preferable as such a single crystal substrate, and quartz, sapphire, magnesium oxide, or the like can be used. Of these, quartz is most preferable because both the crystal structure and the lattice constant are substantially the same as the growing thin film, and the crystal orientation for the substrate surface may be any orientation.

Since an oxide single crystal having a crystal type crystal structure is a low temperature phase, crystallization does not occur by simply performing a temperature rise treatment, or even if it is crystallized, it becomes a different crystal type of a high temperature phase. There is. The addition of an alkali metal such as Li, Na or K has the effect of widening the temperature range in which the crystal structure of the crystal type exists stably. By adding a small amount of these alkali metals to the metal-containing solution, It becomes easy to synthesize an oxide single crystal having

However, since the mixing of alkali metal may impair the characteristics of the oxide single crystal having a crystal type crystal structure, it is desired that the amount thereof be minute. In the present invention, the addition amount of the alkali metal is preferably 3 × 10 ⁻⁴ mol% or more and 5 mol% or less with respect to the amount of metal element in the metal-containing solution.

Among them, Li is particularly preferable because it can expand the temperature region in which the crystal structure of the crystal type is stable in a small amount. Further, since Li has the smallest atomic radius among the alkali metals, its effect on the characteristics of the oxide single crystal having the crystal type crystal structure is smaller than that of other elements. Further, after the single crystal is formed, the electrolytic diffusion treatment for diffusing and removing the metal ions by applying a high-voltage electric field can be performed more effectively with Li than with other elements.

Therefore, Li is most preferable as the alkali metal element added to the metal-containing solution. Most preferred L
The amount of i added is 3 × 10 ^{-2 to} 5 mol%. 3 x 10 ^-2
This is because when the content is 5 mol% or less, the effect of expanding the temperature range in which the crystal structure of the crystal type can stably exist is weak, and when the content is 5 mol% or more, the characteristics of the crystal are significantly deteriorated. Such L
The single crystal thin film crystal produced by the method of the present invention using the i-containing solution also has a concentration of 3 × 10 ^-2 mol% with respect to the total amount of metal elements.
The lithium content is 5 mol% or less.

In order to synthesize a solid by the sol-gel method, it is necessary to control the gelation process of the solution. If the gelation is insufficient, the raw materials may evaporate during the heat treatment process. Conversely, if the gelation proceeds too much, large gel bodies will collect, resulting in gaps between the gel bodies and differences in crystallinity. This is because it becomes difficult to form a dense and high-quality crystal film.

As a method of controlling the gelation process, there is a method of adding various additives to the precursor solution. For example, addition of water can hydrolyze the metal compound in the precursor solution to form a highly active metal hydroxide, and promote gelation by polycondensation between the metal hydroxides.

The amount of water added varies depending on the combination with other additives, but for proper gelation, it should be 0.2 molar equivalent or more and 20 molar equivalents or less with respect to the total amount of metal elements in the metal-containing solution. It is preferable. The reason is that if the amount is less than 0.2 molar equivalent, the promotion of gelation is weak and the raw material is evaporated during the heat treatment, which makes it difficult to form a dense film. Conversely, water 2
If it is added in an amount of 0 mole equivalent or more, gelation will proceed too much, and it will be difficult to apply it uniformly.

Other additives include diethanolamine,
There are diisopropanolamine, triethanolamine, or diethylene glycol. Contrary to water, these additives have a function of lowering the activity of the metal compound by the substitution reaction with the metal compound and stabilizing the whole precursor solution. Therefore, by adding these additives, it is possible to prevent the gelation from progressing too much and suppress the change with time of the precursor.

The amount of diethanolamine, diisopropanolamine, triethanolamine, or diethylene glycol added varies depending on the combination with other additives, but is 0.5 with respect to the total amount of metal elements in the metal-containing solution.
It is preferable that the molar equivalent is 6 or more and 6 or less.
Addition of less than 0.5 molar equivalent does not have the effect of suppressing excessive progress of gelation, and addition of more than 6 molar equivalents does not significantly change the effect, while impurities such as C and N are mixed. Because it will be easier.

In order to maximize the effects of the above-mentioned additives such as alkali metal, water and diethanolamine, it is desirable to use these additives in combination.

[0035]

EXAMPLE A method for producing a single crystal thin film crystal of the present invention by a sol-gel method using a metal alkoxide as a raw material will be described with reference to FIGS. That is, the Y surface (20 × 20 mm) of mirror-polished quartz is used for the single crystal substrate 1, and the single crystal substrate 1 is ultrasonically cleaned in acetone, immersed in 20 wt% hydrochloric acid, and purely cleaned. Then, pretreatment was performed in the order of drying.

As a precursor solution of germanium dioxide,
Ge (OC ₂ H ₅ ) ₄ was dissolved in 100 ml of ethanol to prepare a Ge-containing ethanol solution having a concentration of about 0.5 mol / l, and 2.7 g of water was added. The precursor solution was spin-coated on the single crystal substrate 1 of quartz at 2000 rpm, dried at 200 ° C., and the process of spin coating and drying was repeated 10 times. Then, in an oxygen atmosphere, the temperature is raised to 800 ° C. at a heating rate of 10 ° C./min,
It was crystallized by holding it for 2 hours to form an oxide single crystal film 2 of germanium dioxide on the single crystal substrate 1 as shown in FIG.

Next, as a precursor solution of silicon dioxide,
Si (OC ₂ H ₅ ) ₄ was dissolved in 100 ml of ethanol to prepare a Si-containing ethanol solution having a concentration of about 0.5 mol / l, and 2.7 g of water and 5.257 of diethanolamine were prepared.
0.026 g (1 mol% relative to Si) of LiOC ₂ H ₅ was added.

As shown in FIG. 1, this precursor solution was spin-coated at 2000 rpm on a germanium dioxide oxide single crystal film 2 previously prepared on a single crystal substrate 1, and then dried at 200 ° C. The process of spin coating and drying was repeated 20 times. Then, in an oxygen atmosphere, 10
The temperature is raised to 850 ° C at a heating rate of ° C / min, and 2
It was crystallized by holding for a time to form a single crystal thin film crystal 3.

As shown in FIG. 2, a mirror-polished single crystal Si wafer (diameter 50) is placed on the surface of the single crystal thin film crystal 3 as shown in FIG. It was heated and adhered for 10 minutes. When the whole sample to which the supporting plate 4 was adhered was treated in a 20 wt% hydrochloric acid aqueous solution for 3 hours, the germanium dioxide oxide single crystal film 2 was dissolved and adhered to the supporting plate 4 as shown in FIG. The single crystal thin film crystal 3 that has been peeled off from the single crystal substrate 1.

The obtained single crystal thin film crystal 3 was evaluated by X-ray diffraction, and as a result, it was found that the Y surface of the single crystal thin film crystal having good crystallinity was obtained, and its thickness was 1.8 μm.
Met.

[0041]

According to the present invention, a single crystal thin film crystal having an arbitrary thickness of 5 nm or more and 50 μm or less can be manufactured by the sol-gel method and provided at a low cost without using a large-scale device.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a state in which a single crystal thin film crystal is formed on a single crystal substrate by the method of the present invention.

2 is a schematic cross-sectional view showing a state in which a support plate is bonded to the single crystal thin film crystal of FIG. 1 by the method of the present invention.

FIG. 3 is a schematic cross-sectional view showing a state in which a single crystal thin film crystal having a support plate adhered thereto by the method of the present invention is separated from a single crystal substrate.

[Explanation of symbols]

1 Single crystal substrate 2. Germanium dioxide oxide single crystal film 3 Single crystal thin film crystal 4 Support plate

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-4-264317 (JP, A) JP-A-49-90088 (JP, A) JP-A-5-327383 (JP, A) JP-A 51- 93922 (JP, A) JP 58-190900 (JP, A) JP 61-110773 (JP, A) JP 4-264304 (JP, A) JP 8-213871 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C30B 1/00-35/00 C01B 33/12 CAplus (STN) JSTPlus (JOIS) WPI (DIALOG)

Claims (5)

(57) [Claims] 1. A sol-gel method for oxidization on a single crystal substrate.
An acid having a quartz crystal structure containing germanium as a main component
Oxide single crystal film is formed on the oxide single crystal film.
Single crystal thin film quartz containing silicon dioxide as the main component
After forming the above, the oxide single crystal film is formed in an aqueous solution.
Peel the single crystal thin film crystal from the single crystal substrate by melting
A method for producing a single crystal thin film crystal, characterized by separating . 2. The single crystal substrate is made of quartz.
The method for producing a single crystal thin film crystal according to claim 1 . 3. A metal containing germanium or silicon
In a solution containing 0.2 molar equivalents or more relative to the total amount of metal element
Add 20 mol equivalent or less of water to dissolve the precursor in the sol-gel method.
The liquid is adjusted, The claim 1 or 2 characterized by the above-mentioned.
Method for producing single crystal thin film crystal of . 4. A metal containing germanium or silicon
3 × 10 ⁻² mol% based on the total amount of metal elements in the contained solution
The precursor solution is prepared by adding not less than 5 mol% of lithium.
4. The method according to any one of claims 1 to 3, characterized in that
Method for manufacturing single crystal thin film quartz crystal . 5. A metal containing germanium or silicon
In a solution containing 0.5 molar equivalents or more relative to the total amount of metal element
Diethanolamine and diisopropano of 6 molar equivalents or less
Alcohol, triethanolamine, or diethylene glycol
Characterized by adding a recall to prepare a precursor solution
The single crystal thin film crystal according to any one of claims 1 to 4.
Manufacturing method .