JPH0891977A - Oxide thin film having crystal type crystal structure and method of manufacturing the same - Google Patents

Abstract

(57) [Summary] [Objective] An oxide thin film having a quartz crystal structure of arbitrary thickness and shape can be manufactured at a low cost by a simple method such as hydrothermal synthesis that does not require a large-scale device. To do. [Structure] The thickness per layer formed on the substrate is 5 n
An oxide thin film comprising at least one layer of m to 50 μm, each layer having a quartz crystal structure mainly composed of silicon dioxide, germanium dioxide or a mixture thereof. The oxide thin film having this crystal type crystal structure is formed on the substrate by appropriately controlling the substrate temperature or adding a trace amount of an alkali metal to the raw material by a sol-gel method or a vapor deposition method to form a single crystal substrate. If used, a single crystal thin film can be formed.

Description

Detailed Description of the Invention

[0001]

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

[0002]

Crystals are widely used in oscillators, vibrators, surface acoustic wave devices for high frequency filters, optical waveguides, etc., and are very important industrial materials.

For crystal transformation of silicon dioxide (SiO ₂ ) at normal pressure, in addition to quartz (up to 867 ° C.), tridymite (867 to 1470 ° C.) and cristobalite (147).
0 to 1723 ° C). When these crystals are actually synthesized, they are not necessarily synthesized in an equilibrium state, and various factors such as impurities and temperature control are involved, so that the relationship between the crystal structure and temperature is not always realized. is not.

However, although quartz is the low temperature phase of silicon dioxide crystals, the melting point of silicon dioxide is the transition temperature 867.
Since it is 1730 ° C, which is much higher than 0 ° C, it is said that when it is solidified from a molten state, it becomes glassy, or only a stable crystal structure other than quartz such as cristobalite can be generated in the vicinity of this melting point. In this way, it is not possible to grow quartz by simple high temperature treatment,
It is indispensable to grow at a temperature as low as the transition temperature.

The conventional crystal production method is carried out by a hydrothermal synthesis method in which crystals are grown from an aqueous solution in a high temperature and high pressure state in a closed container, with the intention of growing at a temperature lower than this transition temperature, and particularly silicon dioxide. Taking advantage of the fact that the solubility of Alkali in alkaline solution varies depending on the temperature, a hydrothermal temperature difference method is used to grow a quartz single crystal on a seed crystal from an alkaline solution of silicon dioxide by providing a temperature difference under high temperature and high pressure. Was there. The manufacturing process of crystal by this hydrothermal temperature difference method is
For example, “Ceramics” 15 (1980) No. 3, p.
170-175.

However, since this hydrothermal synthesis method can synthesize only bulky large crystals or granular crystals, it cannot be used as it is for products requiring a thin film shape. Therefore, the crystals actually used as oscillators, oscillators, surface acoustic wave devices for high frequency filters, etc. are currently selected from the large crystal single crystals produced by the hydrothermal temperature difference method in pursuit of mass production effects. It is cut into thin pieces and used.

With the recent increase in communication frequency,
Crystals used as oscillators and vibrators are required to be even thinner. To meet this demand, for example, as disclosed in Japanese Patent Laid-Open No. 5-327383, a technique has been proposed in which a crystal is attached to a semiconductor substrate and polished to process the crystal into a thin film. However, there is a problem that the film thickness obtained by thinning the film by polishing or the like is limited and the cost is increased.

[0008]

The hydrothermal temperature difference method, which is a conventional method for producing quartz, requires a large-scale apparatus for realizing high pressure, and the cost is reduced unless a large crystal is grown by a huge apparatus. Cannot be achieved. Moreover, since it is difficult to form a quartz crystal in an arbitrary shape such as a thin film by this method, a bulky large crystal is processed to form a desired thin film shape in order to form a vibrator or an oscillator. It had to be a crystal.

In particular, with respect to oscillators, vibrators, filters, etc., which are the main applications of quartz, it is required to make the quartz even thinner with the recent increase in the communication frequency. However, in the method of cutting a thin crystal from a large crystal produced by the conventional hydrothermal synthesis method, there is a limit to the thinness of the crystal that can be achieved, and the limit is practically 50 μm.

In view of the above conventional circumstances, the present invention does not require a large-scale apparatus such as a hydrothermal synthesis method, and can easily and inexpensively produce an arbitrary film thickness and shape suitable for an application such as an oscillator or a vibrator. It is an object of the present invention to provide an oxide thin film having a polycrystalline or single crystal quartz crystal structure, which can be obtained as described above, and a manufacturing method thereof.

[0011]

As a method for synthesizing an oxide thin film having a crystal structure of quartz which is a low temperature phase of silicon dioxide, that is, a crystal type crystal structure, the present inventors have adopted a sol-gel method and a vapor deposition method. Adopted, especially by adding a trace amount of alkali metal to the raw material and setting an appropriate temperature condition, it is possible to inexpensively synthesize an oxide thin film having a quartz crystal structure of any shape and thickness by utilizing its chirality. I found a thing.

That is, one of the methods for producing an oxide thin film having a quartz crystal structure provided by the present invention is a sol-gel method, which is prepared from a metal-containing solution containing silicon and / or germanium or a compound thereof. The above precursor solution is applied onto a substrate and heat-treated at a temperature of 500 ° C. or higher and 1200 ° C. or lower, and an oxide thin film having a quartz crystal structure containing silicon dioxide or germanium dioxide or a mixture thereof as a main component from the precursor solution. Is crystallized on the substrate.

Another method of producing the oxide thin film having the crystal structure of the present invention is a vapor deposition method, which uses silicon and / or germanium or a compound thereof as a raw material. Therefore, an oxide thin film having a quartz crystal structure containing silicon dioxide, germanium dioxide, or a mixture thereof as a main component is deposited on the substrate under the condition that the substrate temperature is 400 ° C. or more and 1200 ° C. or less.

Further, by using a single crystal substrate as a substrate in these methods, at least a layer in contact with the substrate can be made into a single crystal and each of the other layers can be made into a single crystal, or crystal orientation can be imparted. .

The oxide thin film having a quartz crystal structure of the present invention produced by each of the above methods is an oxide thin film having at least one layer having a thickness of 5 nm or more and 50 μm or less formed on a substrate. And each layer is mainly composed of silicon dioxide or germanium dioxide or a mixture thereof.

[0016]

The compounds having a crystal structure and exhibiting useful properties such as piezoelectricity include silicon dioxide (SiO ₂ ), germanium dioxide (GeO ₂ ), and oxides having a mixed composition thereof. Therefore, in the present invention, it is necessary that the main component of the oxide thin film is silicon dioxide or germanium dioxide in order to obtain an oxide thin film having a quartz crystal structure with excellent characteristics.

Specifically, the content of silicon or germanium in the oxide thin film or the total thereof is preferably 70 mol% or more, and more preferably 90 mol% or more with respect to the total amount of metal elements. preferable. The content of silicon or germanium or the total thereof is 70 of the total metal elements.
This is because if it is less than mol%, the constitution of the crystal type crystal structure becomes weak and the characteristics of the oxide having the crystal type crystal structure are significantly deteriorated.

It is known that silicon dioxide and germanium dioxide have many kinds of crystal structures in addition to the crystal type crystal structure. For example, in the case of silicon dioxide, in addition to the crystal type, tridymite type, cristobalite type, stishovite type, co-type There is a site type. Moreover, these oxides
Amorphous glass state without crystal structure is very stable. Therefore, in the production of an industrially useful oxide having a crystal type crystal structure, it is important to prevent the crystal structure other than the crystal type and the glass component from being mixed.

Since silicon dioxide has a stable region of a crystal structure of 870 ° C. and a low melting point of 1730 ° C., it does not crystallize or does not crystallize even if it is simply heated. It is difficult to obtain a pure crystal type crystal structure, since the high temperature phase may be a different crystal type. Therefore, in the hydrothermal synthesis method, 100
Crystals are deposited from an alkaline aqueous solution of SiO _{2 under} the conditions of 0 atm and 350 ° C. Thus, although it was difficult to synthesize silicon dioxide having a quartz crystal structure by the sol-gel method of firing under atmospheric pressure or the vapor phase deposition method under reduced pressure, addition of an alkali metal to the raw material, and / or It was found that by mixing germanium dioxide, the quartz crystal structure can be stabilized even by the sol-gel method or the vapor deposition method.

Addition of an alkali metal such as lithium, sodium or potassium has the effect of promoting crystallization of silicon dioxide in the quartz crystal structure and widening the temperature region in which it exists stably. Therefore, for example, by adding a trace amount of an alkali metal to the metal-containing solution in the sol-gel method or to the raw material in the vapor-phase deposition method, it becomes easy to stabilize the obtained oxide having a quartz crystal structure.

However, when the amount of alkali metal in the oxide is large, an oxide not having a crystal type crystal structure is deposited, and the original characteristics of the oxide having a crystal type crystal structure such as dielectric characteristics, piezoelectric characteristics, and temperature stability. Therefore, it is preferable to minimize the addition amount. Specifically, the content of alkali metal is 3 × 10 ^{−4 with} respect to the total amount of metal in the oxide thin film.
It is preferable that the amount is not less than mol% and not more than 10 mol%. When the content of the alkali metal exceeds 10 mol% with respect to the total amount of the metal, the characteristics of the oxide having the crystal type crystal structure are significantly deteriorated, and when it is less than 3 × 10 ^-4 mol%, the crystal type crystal structure is stabilized. This is because the effect becomes weaker. The more preferable content of the alkali metal is 5 × 10 ^-2 mol% or more and 2 mol% or less with respect to the total metal amount.

The alkali metal may be lithium, sodium, potassium, rubidium, cesium or a mixture thereof, and lithium has the greatest effect of stabilizing the quartz crystal structure. Further, since lithium has the smallest atomic radius among the alkali metals, the influence on the characteristics of the oxide having a quartz crystal structure is smaller than that of other elements. Further, the electric field diffusion treatment in which the alkali metal ions are diffused and removed by applying a high-voltage electric field after the oxide is generated, lithium can be more effectively performed than other elements. Therefore, lithium is most preferable as the alkali metal to be added.

Germanium dioxide has a melting point of about 1100 ° C.
And the stable temperature range of the quartz crystal structure is wide,
It is possible to stabilize the quartz crystal structure without adding an alkali metal. Therefore, the effect of adding the alkali metal is remarkable in the oxide containing silicon dioxide as the main component. That is, the addition of an alkali metal is effective when silicon is contained in an amount of 70 mol% or more, more preferably 90 mol% or more, based on the total amount of metal elements.

On the other hand, since the melting point of germanium dioxide is as low as 1100 ° C. and the stable temperature range of the crystal type crystal structure is wide as described above, the crystal type crystal structure is stabilized without adding an alkali metal like silicon dioxide. Can be made. Therefore, an oxide containing a mixture of silicon dioxide and germanium as a main component facilitates the formation of a quartz crystal structure. In order to facilitate the formation of the quartz crystal structure, the molar ratio of germanium to silicon is 0.01.
It is preferably not less than 4 and not more than 0.2, more preferably not less than 0.2 and not more than 1.5. When this molar ratio is less than 0.01, the effect of stabilizing the crystal structure is small, and conversely, when germanium is added in excess of 4, the property of germanium dioxide to dissolve in water becomes remarkable even in the mixture, and it is industrially used as a device material. It is difficult to use as.

In the oxide thin film having a quartz crystal structure of the present invention, alkali metal or germanium can be added to the main component silicon and / or germanium as described above. Various impurity elements such as beryllium, boron, carbon, magnesium, aluminum, phosphorus, calcium, titanium, etc. can be added to improve characteristics such as characteristics and semiconductor characteristics.

The oxide thin film having a quartz crystal structure may be composed of one layer or two or more layers. In order to obtain a thin film having homogeneous and stable characteristics,
Each layer requires a film thickness of 5 nm or more. However, if the film thickness is too thick, the thermal stress may increase and the surface roughness, crystallinity, etc. may decrease. Therefore, in order to obtain stable characteristics, each layer should have a film thickness of 50 μm or less. It is preferable.

Generally, the piezoelectric characteristics of an oxide having a crystal type crystal structure are due to the crystal structure. Therefore,
In order to use the oxide thin film of the present invention for applications such as a vibrator and to fully exhibit its characteristics, it is necessary that the oxide thin film is a single crystal or a polycrystal having a crystallographic orientation.

In order to obtain an oxide thin film having excellent crystallinity as described above, a single crystal substrate is used as the substrate in the method of the present invention so that the crystal structure of the substrate can be controlled by bonding at the interface between the substrate and the thin film. It can be reflected in the crystal structure. That is, by using a single crystal substrate,
Of the two or more layers of oxide thin film, the layer in contact with the substrate can be made into a single crystal, and in the case of two or more layers, each layer can also be a single crystal or a thin film having crystal orientation. Is.

The single crystal substrate is preferably an oxide single crystal, for example, quartz, sapphire, magnesium oxide, strontium titanate, etc. can be used. Of these, quartz is most preferable because it has a crystal structure and a lattice constant that are substantially the same as those of a growing thin film, and is most preferable because the substrate is easily available. The crystal orientation of the substrate surface may be any orientation. In particular, it is most preferable to use the AT surface (JIS standard C6704-1992) as the substrate surface because the temperature stability of the vibration frequency is excellent.

The crystal structure of the oxide may be composed of crystal grains depending on the film forming method and conditions. At this time, in order not to impair the characteristics of the oxide thin film having the crystal structure, the crystal grain size is preferably 500 nm or less. The reason is that if the crystal grains exceed 500 nm, the gap between the crystal grains becomes large, a dense crystal film cannot be obtained, and the characteristics of the oxide thin film are impaired.

Next, the sol-gel method for producing the oxide thin film having the crystal structure of the present invention will be described. A compound soluble in a solvent such as silicon and / or germanium alkoxide is diluted with a solvent such as alcohol into a metal-containing solution, and if necessary, an alkali metal compound,
A precursor solution is prepared by adding water, amine or the like and refluxing the solution. Next, this precursor solution is applied onto the substrate by spin coating or dip coating. Finally, the substrate coated with the precursor solution is heat-treated to evaporate the solvent or the like to cause gelation and solidification and further crystallization.

The sol-gel method can give an arbitrary shape for performing coating in a solution state and can easily form a thin film. Further, the film thickness can be adjusted by film forming conditions such as the viscosity of the precursor solution, the number of rotations of the substrate at the time of coating or the pulling speed, and the film formation can be repeated until the required film thickness is obtained. It is also possible to stack a plurality of oxide thin films having different compositions by changing the applied precursor solution.

The heat treatment needs to be performed at a temperature at which the crystal structure is crystallized. The temperature is in the range of 500 to 1200 ° C., though it depends on the amount of alkali metal added. Specifically, 800 in the case of silicon dioxide
The temperature is preferably in the range of to 1200 ° C, and in the case of germanium dioxide, the range of 500 to 1000 ° C is preferable. In addition, in the case where both oxides are mixed, it is 50% wider than in the case of a single composition.
The temperature may be in the range of 0 to 1200 ° C, but the higher the content of silicon dioxide, the higher the heat treatment temperature.

The heat treatment temperature is set in the range of 500 to 1200 ° C. because crystallization does not occur below 500 ° C., the crystallinity is poor even when crystallization occurs, and organic groups contained in the raw materials remain. Because there is. Also, if the temperature exceeds 1200 ° C., another type of crystal structure of the high temperature phase is likely to be formed. Further, the heat treatment is preferably performed in an oxygen atmosphere or an oxygen atmosphere containing water vapor, or in the air or in an atmosphere containing water vapor.

Metal compounds used as raw materials for the sol-gel method include Si (OCH ₃ ) ₄ , Si (OC ₂ H ₅ ) ₄ and Si (O
_{C 3 H 7) 4, Ge} (OCH 3) 4, Ge (OC 2 H 5) 4, Ge (O
C ₃ H ₇ ) ₄ etc. metal alkoxide, Si (COCH ₂ COC
Examples thereof include metal acetyl acetate such as H ₃ ), metal halide such as SiCl _{4, and the} like. In the case of the sol-gel method,
Alkali metal is added as the example LiOC ₂ H ₅ and NaOC ₂ H ₅ and the like.

To synthesize a solid by the sol-gel method,
It is necessary to control the gelling 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 crystallinity. This is because there is a difference and it becomes difficult to form a dense and high-quality oxide thin film. However, depending on the type of raw material and film forming conditions, if there is no evaporation during heat treatment or the prepared metal-containing solution has already gelled properly, the metal-containing solution may be used as it is as the precursor solution. it can.

Control of the gelation process is carried out by refluxing the metal-containing solution or adding various additives such as water. That is, by adding water, the metal compound in the metal-containing solution is hydrolyzed to form a highly active metal hydroxide, and polycondensation can accelerate gelation. The amount of water added varies depending on the combination with other additives, but for proper gelation, it is preferably 0.2 mol equivalent or more and 20 mol equivalents or less with respect to 1 mol of all metal elements in the metal-containing solution. The reason is,
If it is less than 0.2 molar equivalent, the gelation is weakly promoted and the raw material is evaporated during the heat treatment to make it difficult to form a dense film.
This is because if it is added in an amount exceeding 0 molar equivalent, gelation will proceed too much, making uniform coating difficult.

On the other hand, examples of additives used for suppressing gelation include diethanolamine, diisopropanolamine, triethanolamine, and ethylene glycol. These additives have the function of reducing the activity of the metal compound by the substitution reaction with the metal compound and stabilizing the 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 addition amount of these additives varies depending on the combination with other additives, but is preferably 0.5 mol equivalent or more and 6 mol equivalents or less per 1 mol of all metal elements in the metal-containing solution. The reason is that if the addition amount is less than 0.5 molar equivalent, there is no effect of suppressing excessive progress of gelation, and conversely, if the addition amount exceeds 6 molar equivalent, the effect of suppressing excessive progress of gelation changes significantly. On the other hand, impurities such as carbon and nitrogen tend to remain, while there is no such phenomenon. Further, in order to maximize the effect of additives such as alkali metal, water and diethanolamine, it is preferable to use these additives in combination.

Next, the vapor deposition method for producing the oxide thin film having the crystal structure of the present invention will be described. Typical examples of the vapor deposition method are a CVD method, a sputtering method, a vapor deposition method, a laser abrasion method and the like. In any of these methods, a raw material containing silicon and / or germanium is used, and if necessary, this raw material is used. It is possible to form an oxide thin film having a crystal type crystal structure on the substrate from the vapor phase by adding and containing one or more kinds of alkali metals and controlling the substrate temperature.

First, the substrate temperature in the vapor deposition method is 40.
It shall be in the range of 0 to 1200 ° C. Specifically, depending on the amount of the alkali metal added, 600 to 600 in the case of silicon dioxide.
The range of 1200 ° C is preferable, and in the case of germanium dioxide, the range of 400 to 1000 ° C is preferable. In addition, the mixed oxide of both is 400 to 400 times wider than the case of a single composition.
Although it is in the range of 1200 ° C., the substrate temperature rises as the content of silicon dioxide increases.

In the CVD method among the vapor deposition methods, a vaporizable compound containing silicon and / or germanium is used as a raw material. For example, Si (OCH ₃ ) ₄ , Si
(OC ₂ H ₅ ) ₄ , Si (OC ₃ H ₇ ) ₄ , Ge (OCH ₃ ) ₄ , Ge
A metal alkoxide such as (OC ₂ H ₅ ) ₄ or Ge (OC ₃ H ₇ ) ₄ ;
Organometallic compounds such as Si (CH ₃ ) ₄ and SiH ₄ , SiH ₂ C
Examples thereof include metal halides such as l ₂ , SiCl ₄ , and GeCl ₄ . The alkali metal is, for example, LiOC ₂ H ₅
Or NaOC ₂ H ₅ or the like.

Further, in the CVD method, it is necessary to mix an oxidizing gas with the above metal-containing raw material to form an oxide. As the oxidizing gas, oxygen, carbon dioxide, nitrous oxide, steam or the like can be used. An oxide thin film is formed by diluting these raw materials with a diluting gas and introducing them onto the heated substrate in the film forming chamber. As a diluent gas,
Hydrogen, inert gas, nitrogen, etc. are used. When the pressure in the film forming chamber is less than 0.01 Torr, the growth rate of the film is slow, which is not practical. When the pressure exceeds atmospheric pressure, the film forming apparatus used becomes very expensive. preferable. Incidentally, in order to accelerate the decomposition of the raw material gas, a plasma CVD method or a photo CVD method which is one of the CVD methods is used.
The law is valid.

In the sputtering method, a metal of silicon and / or germanium or an oxide having a desired composition is targeted. In the case of an oxide target, an inert gas, for example, Ar, He, Ne, or the like may be used as the sputtering gas, but in the case of a metal target, the inert gas is an oxygen-containing gas such as O ₂ , N ₂ O, or CO. _It is necessary to use a sputter gas that is a mixture of the _two . The pressure inside the deposition chamber is 1
0 Torr or less is preferable, 0.0001 to 10 Tor
Ions can be generated in the range of r. DC is used as a sputtering method in which an electric field is applied to generate ions.
Method, RF method, and ion beam method, all of which can be used similarly.

In the vapor deposition method, SiO ₂ and Si are used as raw materials.
It is preferable to use oxides such as O, GeO ₂ , and Li ₂ O. When using a metal raw material, it is necessary to separately introduce oxygen or an oxygen-containing gas into the film forming chamber. The pressure in the film forming chamber is 10 Torr or less, preferably 0.01 Torr.
Below. As a modification of the vapor deposition method, there are an MBE method, an ion plating method, an activated reaction vapor deposition method, an arc type ion plating method and the like, and any of them can be used in the same manner.

The laser abrasion method is a method of irradiating a raw material with a pulsed or continuously focused laser beam to instantaneously evaporate a minute portion of the raw material, and the obtained film composition is almost the same as that of the raw material. There are advantages. That is, it is suitable for the method of the present invention because of its excellent composition controllability. Therefore, an oxide having a fixed composition is used as the raw material. The laser used is preferably one having a short wavelength and a high energy density, and specifically, an excimer laser (ArF, KrF, KrCl, XeCl), a YAG laser or the like can be used. Further, in order to maintain the denseness of the oxide thin film, the pressure in the film forming chamber is set to 10 Torr or less.

[0047]

Example 1 A silicon dioxide thin film was formed on a quartz glass substrate by a sol-gel method using a metal alkoxide as a raw material. The quartz glass substrate was mirror-polished, ultrasonically washed with acetone, and then pretreated in the order of immersion treatment in 20 wt% hydrochloric acid, pure water washing, and drying.

On the other hand, the precursor solution of the sol-gel method was prepared by the following procedure. 10.41 in 100 ml ethanol
7 g of Si (OC ₂ H ₅ ) ₄ was dissolved to give a concentration of 0.5 mol /
l of silicon-containing ethanol solution was prepared and
g water, 5.27 g diethanolamine and 0.026
g of LiOC ₂ H ₅ was added to obtain a precursor solution.

This precursor solution was spin-coated on the quartz glass substrate at 2000 rpm, and then 900 ° C. at a heating rate of 10 ° C./min in an oxygen atmosphere containing water vapor.
And heated at 900 ° C. for 2 hours to perform heat treatment.

To evaluate the crystallinity of the obtained thin film, θ
As a result of observing X-ray diffraction by the -2θ method, only an amorphous diffraction peak generated from the silica glass substrate and a polycrystalline diffraction peak of quartz generated from the thin film were observed at around 20 °, and a silicon dioxide polycrystal having a quartz crystal structure was observed. It was found that a crystal thin film was formed.

Comparative Example 1 Pretreatment of a substrate, preparation of a precursor solution, and formation of a thin film were performed in the same procedure as in Example 1 except that water was not added when preparing a precursor solution. Observation of the thin film obtained by the heat treatment revealed that a dense thin film was not formed.

Comparative Example 2 Pretreatment of a substrate, preparation of a precursor solution, and formation of a thin film were performed in the same procedure as in Example 1 except that the amount of water was adjusted to 25 g when preparing a precursor solution. However, even if the precursor solution was applied onto the substrate, uniform application was not possible, and only a non-uniform thin film was obtained.

Example 2 Except that the AT surface (JIS standard C6704-1922) of a quartz single crystal substrate subjected to mirror polishing was used as the substrate,
Pretreatment of the substrate, preparation of the precursor solution, and formation of a thin film were performed in the same procedure as in Example 1 above. The thin film formed on the quartz single crystal substrate was evaluated by X-ray diffraction in the same manner as in Example 1. As a result, no diffraction peak of an amorphous component generated at a low angle (up to 20 °) was observed, and a thin film other than the quartz AT plane was observed. Since no diffraction peak was observed, it was found that a quartz single crystal thin film was formed. This quartz single crystal thin film had a film thickness of 80 nm, and the thin film contained 1 mol% of the total amount of metal, lithium.

Comparative Example 3 Pretreatment of a substrate, preparation of a precursor solution, and formation of a thin film were performed in the same procedure as in Example 2 except that the heat treatment temperature at the time of forming a thin film was 350 ° C. The thin film formed on the quartz single crystal substrate was evaluated by X-ray diffraction in the same manner as in Example 1. As a result, an amorphous diffraction peak generated at around 20 ° and a diffraction peak of the quartz AT surface generated from the quartz substrate were observed. Therefore, it was found that an amorphous thin film of silicon dioxide was formed.

Comparative Example 4 Except that the heat treatment temperature during thin film formation was 1250 ° C.
Pretreatment of the substrate, preparation of the precursor solution, and formation of a thin film were performed in the same procedure as in Example 2. The thin film formed on the quartz single crystal substrate was evaluated by X-ray diffraction in the same manner as in Example 1. As a result, diffraction peaks of the cristobalite type crystal and diffraction peaks of the quartz AT surface generated from the quartz substrate were observed. It was found that a thin film of cristobalite type crystal which is a high temperature phase of silicon dioxide was formed.

Comparative Example 5 Pretreatment of the substrate, preparation of the precursor solution, and formation of a thin film were carried out in the same procedure as in Example 2 except that LiOC ₂ H ₅ was not added when preparing the precursor solution. . The thin film formed on the quartz single crystal substrate was evaluated by X-ray diffraction in the same manner as in Example 1. As a result, an amorphous diffraction peak generated at around 20 ° and a diffraction peak of the quartz AT surface generated from the quartz substrate were observed. Therefore, it was found that an amorphous thin film of silicon dioxide was formed.

Comparative Example 6 The amount of LiOC ₂ H ₅ added at the time of preparing the precursor solution was adjusted to 0.
Pretreatment of the substrate, preparation of the precursor solution, and formation of a thin film were performed in the same procedure as in Example 2 except that the amount was 52 g. The thin film formed on the quartz single crystal substrate was evaluated by X-ray diffraction in the same manner as in Example 1. As a result, diffraction peaks on the AT surface of the quartz crystal and respective diffraction peaks of Li ₂ Si ₂ O ₅ produced by firing were observed. It was found that Li ₂ Si ₂ O ₅ was mixed in the thin film.

Example 3 A germanium dioxide thin film was formed on a quartz single crystal substrate by a sol-gel method using a metal alkoxide as a raw material. As the single crystal substrate, a mirror-polished crystal (001) plane (Z plane) was used, and after ultrasonic cleaning with acetone, pretreatment was performed in the order of immersion treatment in 20 wt% hydrochloric acid, pure water cleaning, and drying. .

On the other hand, the precursor solution of the sol-gel method was prepared by the following procedure. 12.65 in 100 ml ethanol
g of Ge (OC ₂ H ₅ ) ₄ was dissolved to give a concentration of 0.5 mol / l.
Germanium-containing ethanol solution was prepared, and 0.5 g of water was added thereto to prepare a precursor solution.

The precursor solution was spin-coated on the quartz single crystal substrate at 2000 rpm, and then heated to 500 ° C. at a temperature rising rate of 10 ° C./min in the atmosphere to 500 ° C.
And held for 2 hours for heat treatment.

To evaluate the crystallinity of the obtained thin film, θ
As a result of observing the X-ray diffraction by the −2θ method, as shown in FIG. 1, no diffraction peak of an amorphous component generated at a low angle (up to 20 °) was observed, and the Z plane of germanium dioxide having a quartz crystal structure and the quartz crystal. A diffraction peak on the Z plane of the single crystal substrate was observed. Further, as shown in FIGS. 2 and 3, Z
As a result of observing the diffraction of the (104) plane of the germanium dioxide having a quartz crystal structure and the (104) plane of the quartz single crystal substrate by rotating around the axis, it was found that the dioxide having a quartz crystal structure at the same angle as the quartz single crystal substrate. Since the diffraction of germanium could be observed, it was found that a germanium dioxide single crystal thin film having a crystal type crystal structure was formed. The thickness of the germanium dioxide single crystal thin film having this crystal type crystal structure was 65 nm.

Example 4 A thin film of a mixture of silicon dioxide and germanium dioxide was formed on a quartz single crystal substrate by a sol-gel method using a metal alkoxide as a raw material. As the single crystal substrate, mirror-polished (110) plane (X plane) of crystal was used, and after ultrasonic cleaning with acetone, pretreatment was performed in the order of immersion treatment in 20 wt% hydrochloric acid, pure water cleaning, and drying. .

On the other hand, the precursor solution of the sol-gel method was prepared by the following procedure. 6.32 g in 100 ml of ethanol
Ge (OC ₂ H ₅ ) ₄ and 3.806 g of Si (OCH ₃ ) ₄ were dissolved to prepare an ethanol solution containing silicon and germanium at each concentration of 0.25 mol / l, to which 9 g of water was added. Added to give a precursor solution.

This precursor solution was spin-coated on the quartz single crystal substrate at 2000 rpm, and then heated to 1000 ° C. in the atmosphere at a temperature rising rate of 10 ° C./minute to obtain 100
It heat-processed by hold | maintaining at 0 degreeC for 2 hours.

To evaluate the crystallinity of the obtained thin film, θ
As a result of observing X-ray diffraction by the -2θ method, a low angle (~ 20
No diffraction peak of the amorphous component generated in (3) is observed, and the X-plane of the mixture of both having the crystal-type crystal structure formed between the X-plane of germanium dioxide having the crystal-type crystal structure and the X-plane of the crystal, and the crystal A diffraction peak on the X-plane of the single crystal substrate was observed. Furthermore, as a result of observing the diffraction of the (211) plane of the mixture having the crystal type crystal structure and the (211) plane of the crystal single crystal substrate by rotation around the X axis, the crystal type crystal structure was formed at the same angle as the crystal single crystal substrate. From the fact that the diffraction of the mixture having the above was observed, it was found that a single crystal thin film of a mixture of silicon dioxide and germanium dioxide having a crystal structure was formed.

The thickness of the single crystal thin film of the mixture of silicon dioxide and germanium dioxide having the crystal structure is 7
It was 0 nm. Also, from the result of electron fluorescent X-ray analysis, it was found that the composition of this thin film was Si: Ge = 1: 1.01. When the structure of the single crystal thin film of this mixture was observed with a transmission electron microscope, the crystal grain size was 20 n.
A crystal structure of m was observed.

Example 5 10 by a sol-gel method using a metal alkoxide as a raw material
It was formed by laminating a mixture thin film of silicon dioxide and germanium dioxide and a germanium dioxide thin film on a quartz single crystal substrate of mm square. As the single crystal substrate, a mirror-polished crystal (001) plane (Z plane) was used, and after ultrasonic cleaning with acetone, pretreatment was performed in the order of immersion treatment in 20 wt% hydrochloric acid, pure water cleaning, and drying. .

On the other hand, the precursor solution of the sol-gel method was prepared by the following procedure. 6.32 g in 100 ml of ethanol
Ge (OC ₂ H ₅ ) ₄ and 3.806 g of Si (OCH ₃ ) ₄ were dissolved to prepare an ethanol solution containing silicon and germanium at each concentration of 0.25 mol / l, to which 9 g of water was added. The precursor solution A was added. Also, 12.65 g of Ge (OC ₂ H ₅ ) ₄ was dissolved in 100 ml of ethanol,
A germanium-containing ethanol solution having a concentration of 0.5 mol / l was prepared, and 0.5 g of water was added thereto to prepare a precursor solution B.
And

Next, the precursor solution A containing silicon and germanium was spin-coated on the quartz single crystal substrate at 2000 rpm, dried at 300 ° C. for 10 minutes, and the same coating and drying steps were repeated 20 times. It was
Then, in an oxygen atmosphere, it was heated to 1000 ° C. at a temperature rising rate of 10 ° C./min, and held at 1000 ° C. for 2 hours to perform heat treatment.

On the substrate thus formed with the thin film, the precursor solution B containing germanium was continuously added at 2000 r.
After spin coating with pm, it was dried at 300 ° C. for 10 minutes, and the same coating and drying steps were repeated 20 times. After that, heating was performed in an oxygen atmosphere at a heating rate of 10 ° C./min to 500 ° C., and the temperature was kept at 500 ° C. for 2 hours to perform heat treatment.

The obtained thin film had a shape of a 10 mm square, which was as a substrate. The crystallinity of this thin film was evaluated by X-ray diffraction as in Example 4. As a result, as shown in FIG. 4, crystals, a mixture of silicon dioxide and germanium dioxide having a crystal type crystal structure, and a crystal type crystal structure were confirmed. Each diffraction peak of the Z plane of germanium dioxide contained therein was observed. From this, it was found that a thin film in which a single crystal layer of a mixture of silicon dioxide and germanium dioxide having a crystal type crystal structure and a single crystal layer of germanium dioxide having a crystal type crystal structure were laminated was formed. .

The thickness of the single crystal layer of the mixture of silicon dioxide and germanium dioxide having the crystal structure is 1.
The thickness of the single crystal layer of germanium dioxide having a crystal structure of 4 μm was 1.3 μm. Also, electronic fluorescence X
From the result of the line analysis, it was found that the composition of the mixture single crystal layer of silicon dioxide and germanium dioxide was Si: Ge = 1: 1.01.

Example 6 A mixed oxide thin film of silicon dioxide and germanium dioxide was formed on a quartz single crystal substrate by a plasma CVD method using a metal alkoxide as a raw material. As the single crystal substrate, mirror-polished (001) plane (Z plane) of quartz was used, and pretreatment was carried out in the order of ultrasonic cleaning with acetone, dipping in 20 wt% hydrochloric acid, pure water cleaning, and drying. .

First, after evacuating the inside of the reaction vessel to a high vacuum,
The quartz single crystal substrate placed on the substrate support was held at 800 ° C., and the raw material gas was introduced into the reaction vessel. Source gas is 30
Si (OC ₂ H ₅ ) ₄ kept at ℃ and Ge kept at 35 ℃
(OC ₂ H ₅ ) ₄ was used and supplied by a carrier gas of Ar at a flow rate of 5 sccm (standard cubic centimeter / minute) and 10 sccm, respectively. At the same time, 5 sccm of oxygen is used as an oxidizing gas and 500 s of Ar gas is used as a diluent gas.
The pressure in the reaction vessel was maintained at 0.5 Torr. On a circular electrode provided parallel to the substrate support 13.
A high-frequency electric field of 56 MHz of 300 W was applied to react the raw material gas to form a film for 2 hours.

To evaluate the crystallinity of the obtained thin film, θ
As a result of observing the X-ray diffraction by the −2θ method, as shown in FIG. 5, no diffraction peak of an amorphous component generated at a low angle (up to 20 °) was observed, and the Z plane of the crystal and the dioxide having the crystal type crystal structure were observed. Z of a mixture of silicon and germanium dioxide
Each diffraction peak of the surface was observed. From this, it was found that a single crystal thin film of a mixture of silicon dioxide and germanium dioxide having a crystal structure was formed.
The single crystal thin film of this mixture had a thickness of 0.5 μm, and the composition of the thin film was Si: G from the results of electron fluorescence X-ray analysis.
It was found that e = 1: 0.93.

Example 7 A silicon dioxide thin film was formed on a silicon single crystal substrate by the sputtering method. As the single crystal substrate, mirror-polished silicon (001) plane was used, and ultrasonic cleaning with acetone was performed.
Pretreatment was performed in the order of dipping treatment in 0 wt% hydrochloric acid, washing with pure water, and drying. Further, as a sputtering target, quartz glass having a Li / Si molar ratio of 0.7 mol% was prepared and used by a sol-gel method using Si (OC ₂ H ₅ ) ₄ and LiOC ₂ H ₅ as raw materials.

First, after evacuating the inside of the reaction vessel to a high vacuum,
The silicon single crystal substrate placed on the substrate support was heated to 850 ° C., and a mixed gas of 80% by volume Ar and 20% by volume O ₂ was introduced into the reaction vessel so that the pressure was 0.02 Torr. High frequency electric field of 13.56MHz on the target side 3
00 W was applied, and the film was formed by magnetron sputtering for 1 hour.

To evaluate the crystallinity of the obtained thin film, θ
As a result of observing X-ray diffraction by the -2θ method, only a diffraction peak generated from the silicon single crystal substrate and a polycrystalline diffraction peak of the crystal generated from the thin film are observed, and a polycrystalline thin film of silicon dioxide having a crystal type crystal structure is formed. It turned out that it was done. The thickness of this silicon dioxide polycrystal thin film is 0.1.
It was 3 μm, and it was found that the molar ratio of Li / Si in the thin film was 0.9 mol%.

Example 8 A silicon dioxide thin film was formed on a sapphire single crystal substrate by a vapor deposition method using a lithium-containing quartz glass prepared by a sol-gel method as a raw material as in the case of Example 7 above. As the single crystal substrate, a mirror-polished (001) surface of sapphire was used, and pretreatment was performed in the order of ultrasonic cleaning with acetone, immersion treatment in 20 wt% hydrochloric acid, pure water cleaning, and drying.

The target of the quartz glass containing lithium was set in the electron beam heating type evaporation source in the vapor deposition apparatus, the inside of the reaction vessel was evacuated to a high vacuum, and the sapphire substrate was set at 950.
Heated to ° C. After that, oxygen was introduced as an oxidizing gas until the pressure became 5 × 10 ⁻⁵ Torr, and film formation was performed for 30 minutes while the target of lithium-containing silica glass was heated and evaporated by an electron beam.

To evaluate the crystallinity of the obtained thin film, θ
As a result of observing X-ray diffraction by the -2θ method, a diffraction peak generated from a sapphire substrate and a diffraction peak oriented in the (001) axis of quartz are observed, and a thin film oriented in the (001) axis of silicon dioxide having a quartz crystal structure. Was found to have been formed. The thickness of this silicon dioxide thin film was 0.06 μm.

Example 9 A germanium dioxide thin film was formed on a quartz single crystal substrate by the laser abrasion method. As the single crystal substrate, a mirror-polished quartz AT surface was used, and pretreatment was performed in the order of ultrasonic cleaning with acetone, immersion treatment in 20 wt% hydrochloric acid, pure water cleaning, and drying. Further, as an abrasion target, germanium dioxide glass was prepared and used by a sol-gel method using Ge (OC ₂ H ₅ ) ₄ as a raw material.

First, a quartz single crystal substrate was placed on the substrate support of the reaction container, and the distance between the substrate and the target was set to 5 cm. Oxygen was added as 0.03T as an oxidizing gas in the reaction vessel.
After introducing the orr, the quartz single crystal substrate was heated to 670 ° C. An ArF excimer laser (193 nm) is used as a pulse laser, the laser light is focused on a target by a spherical convex lens, and energy laser light having an energy of 150 mJ per pulse is irradiated at a frequency of 5 pulses per second for 15 minutes. The membrane was made.

To evaluate the crystallinity of the obtained thin film, θ
As a result of observing X-ray diffraction by the -2θ method, a diffraction peak of AT plane of quartz and a diffraction peak of AT plane of germanium dioxide having a crystal type crystal structure were observed, and a single crystal of germanium dioxide having a crystal type crystal structure was observed. It was found that a thin film was formed. The maximum thickness of this germanium dioxide single crystal thin film was 1 μm.

[0085]

According to the present invention, the thickness is 5 nm or more and 50 or more.
It is possible to provide an oxide thin film having a crystal type crystal structure with an arbitrary thickness of μm or less by a sol-gel method that does not require a large-scale device or a vapor deposition method that is excellent in controllability and can be provided at low cost.

[Brief description of drawings]

FIG. 1 is a graph showing X-ray diffraction peaks of a quartz single crystal substrate (Z plane) and a germanium dioxide thin film formed thereon in Example 3.

FIG. 2 is a graph showing an X-ray diffraction peak around a Z axis of a crystal (104) axis which is a substrate in Example 3.

FIG. 3 is a graph showing an X-ray diffraction peak around a Z axis of germanium dioxide (104) axis having a quartz crystal structure in Example 3.

FIG. 4 shows a quartz single crystal substrate (Z plane) in Example 5,
It is a graph which shows the X-ray-diffraction peak of the thin film which laminated | stacked the mixture layer of the silicon dioxide and germanium dioxide formed on it, and the germanium dioxide layer.

FIG. 5 shows a quartz single crystal substrate (Z plane) in Example 6,
It is a graph which shows the X-ray-diffraction peak of the mixture thin film of silicon dioxide and germanium dioxide formed on it.

Claims (14)

[Claims] 1. An oxide thin film comprising at least one layer having a thickness of 5 nm or more and 50 μm or less formed on a substrate, each layer containing silicon dioxide or germanium dioxide or a mixture thereof as a main component. An oxide thin film having a quartz crystal structure characterized by the above. 2. In an oxide thin film having a quartz crystal structure, 70 mol% or more of silicon based on the total amount of metal elements,
The oxide thin film having a quartz crystal structure according to claim 1, which contains 3 × 10 ⁻⁴ mol% to 10 mol% of an alkali metal. 3. The total content of silicon and germanium in the oxide thin film having a crystal structure is 70 mol% or more based on the total amount of metal elements, and the molar ratio of germanium to silicon is 0.01 or more. It is 4 or less, The oxide thin film which has a crystal type crystal structure of Claim 1 characterized by the above-mentioned. 4. The substrate is a single crystal substrate, at least a layer in contact with the substrate is a single crystal, and each of the other layers is a single crystal or has crystal orientation. 3. An oxide thin film having the crystal structure of quartz according to any one of 3 above. 5. The oxide thin film having a quartz crystal structure according to claim 4, wherein the single crystal substrate is a quartz single crystal. 6. A precursor solution prepared from a metal-containing solution containing silicon and / or germanium or a compound thereof by a sol-gel method is applied onto a substrate and heat-treated at 500 ° C. or higher and 1200 ° C. or lower to give a precursor. A method for producing an oxide thin film having a crystal type crystal structure, which comprises crystallizing an oxide thin film having a crystal type crystal structure containing silicon dioxide or germanium dioxide or a mixture thereof as a main component from a solution on a substrate. 7. When the metal-containing solution used for preparing the precursor solution by the sol-gel method contains 70 mol% or more of silicon with respect to the total amount of metal elements, the metal-containing solution contains 3 × 10 ⁻⁴ mol% or more 10 The method for producing an oxide thin film having a quartz crystal structure according to claim 6, wherein the precursor solution is adjusted by adding an alkali metal in an amount of mol% or less. 8. When the total content of silicon and germanium in the metal-containing solution used for the preparation of the precursor solution by the sol-gel method is 70 mol% or more based on the total amount of metal elements, the metal-containing solution contains The method for producing an oxide thin film having a quartz crystal structure according to claim 6, characterized in that the precursor solution is adjusted such that the molar ratio of germanium to silicon is 0.01 or more and 4 or less. 9. When preparing a precursor solution by the sol-gel method, the metal-containing solution contains 0.1 mol of the total amount of metal elements.
2 molar equivalents or more and 20 molar equivalents or less of water, and / or 0.5 molar equivalents or more and 6 molar equivalents or less of diethanolamine, diisopropanolamine, triethanolamine, or diethylene glycol is added to 1 mole of the total metal elements. , Characterized in that the precursor solution is prepared,
A method for producing an oxide thin film having a crystal structure according to claim 6. 10. A vapor phase deposition method is used to obtain a substrate having a substrate temperature of 400 ° C. or higher and 1200 ° C. or lower from a vapor phase using silicon and / or germanium or a compound thereof as a raw material.
A method for producing an oxide thin film having a crystal type crystal structure, comprising depositing at least one oxide thin film having a crystal type crystal structure, which comprises silicon dioxide, germanium dioxide or a mixture thereof as a main component, on a substrate. 11. When the raw material by the vapor deposition method contains 70 mol% or more of silicon with respect to the total amount of metal elements, an alkali metal of 3 × 10 ⁻⁴ mol% or more and 10 mol% or less is further added to the raw material. The method for producing an oxide thin film having a quartz crystal structure according to claim 10, which is used. 12. The total content of silicon and germanium in the raw material used in the vapor deposition method is 7 with respect to the total amount of metal elements.
The oxide thin film having a crystal structure according to claim 10, characterized in that when it is 0 mol% or more, the molar ratio of germanium to silicon in the raw material is 0.01 or more and 4 or less. Method. 13. A single crystal is used as a substrate, at least a layer in contact with the substrate is a single crystal, and each of the other layers is a single crystal, or crystal orientation is imparted. 13. The method for producing an oxide thin film having a crystal structure according to any one of 12. 14. The method for producing an oxide thin film having a quartz crystal structure according to claim 13, wherein the single crystal substrate is a quartz single crystal.