JP2001116943A - Method for manufacturing metal oxide thin film element - Google Patents

Abstract

(57) [PROBLEMS] To provide a method for producing a metal oxide thin film element having higher productivity and good characteristics, particularly a ferroelectric thin film element. An object of the present invention is to provide a method of manufacturing a ferroelectric thin-film element capable of efficiently forming a fine pattern having good characteristics and producing a wide range of ferroelectric thin-film elements with high productivity. A step of forming an amorphous metal oxide thin film containing lead in excess of a stoichiometric composition as a second layer on a first layer, and etching the amorphous metal oxide thin film A method for manufacturing a metal oxide thin film element, comprising: a step of crystallizing the etched amorphous metal oxide thin film by heating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a metal oxide thin film element, and more particularly to a method for manufacturing various ferroelectric thin film elements such as various switching elements, modulation elements, filter elements, and deflection elements. The present invention relates to a method, and provides a method for easily providing a fine pattern such as a channel optical waveguide or a grating having good characteristics.

[0002]

2. Description of the Related Art Planar waveguide materials include glass such as quartz, ferroelectric or electro-optical materials such as LiNbO ₃ , magneto-optical materials such as Y ₃ Ga ₅ O ₁₂ , polymers such as PMMA, and GaAs-based materials. Is used. Among these, for example, a material having a good acousto-optic effect or an electro-optic effect is an oxide ferroelectric material such as LiNbO ₃ , and most of the devices actually manufactured using these effects are LiNbO _3. It is. Strong addition to BaTiO ₃ of LiNbO ₃ as _{dielectric, PbTiO 3, Pb 1-x} La x (Zr y Ti 1-y) 1-x / 4 O 3 (x and y PZT by the value of, PLT, PLZT) , Pb (Mg _1/3 Nb _2/3 ) O ₃ ,
KNbO ₃ , LiTaO ₃ , Sr _x Ba _1-x Nb ₂ O ₆ , Pb _x Ba _1-x Nb ₂ O ₆ , Bi ₄ Ti
There are many materials such as ₃ O ₁₂ , Pb ₂ KNb ₅ O ₁₅ , K ₃ Li ₂ Nb ₅ O _15, and many of these materials have better properties than LiNbO ₃ . In _{particular, Pb 1-x La x (} Zr y Ti 1-y) 1-x / 4 O 3 is Li
Known as a material having a much higher electro-optic coefficient than NbO _{3, the} electro-optic coefficient of LiNbO ₃ single crystal is 30.9 pm / V, whereas PLZT (8/65/35: x = 8%, y = 65%, 1-y = 35%) The electro-optic coefficient of ceramics is 612 pm / V.
LiNbO ₃ despite ferroelectric often have better properties than actually fabricated elements Ya almost LiNbO ₃
What using LiTaO _3, except LiNbO ₃ and LiTaO _3, which has established optical waveguide technology by Ti diffusion and proton exchange to the single crystal growth technology and its wafer must perform epitaxial growth of a thin film, the conventional air In some cases, thin-film optical waveguides of practical quality could not be produced by phase growth.

On the other hand, the present inventors have invented a method for producing a thin film optical waveguide of a practical level by a solid phase epitaxial growth technique for producing a thin film optical waveguide of a practical level (Japanese Patent Laid-Open No. 7-78508). This solves the problem that an optical waveguide of a practical level of quality could not be manufactured. However, even though epitaxial thin-film optical waveguides could be manufactured, there was no technology for manufacturing good fine patterns such as channel optical waveguides and gratings, and almost all devices actually manufactured use LiNbO ₃ or LiTaO _3. That is one big reason. That is, for LiNbO _{3 and the} like, a method for producing a three-dimensional (channel) optical waveguide or grating using Ti diffusion or proton exchange technology is described in Nishihara, Haruna, Suhara, Optical Integrated Circuits, Ohmsha (1993) pp. 195-23.
As shown in Fig. 0, other materials, especially Pb _{1-x
La x (Zr y Ti 1-} y) in _{1-x / 4} O ₃ not known how to ion exchange or diffusion of other elements.

Also, in order to produce an optical waveguide in LiNbO ₃ or LiTaO ₃ by diffusing Ti or proton in a single crystal wafer, the effective refractive index of the channel optical waveguide cannot be made sufficiently higher than the effective refractive index around it. Since the refractive index difference cannot be increased, it is necessary to increase the curvature of the S-shaped channel optical waveguide, and the size of the matrix optical switch is also an issue. On the other hand, for quartz optical waveguides, etc., a method of producing a channel optical waveguide etc. by reactive ion etching has been proposed by Kawachi, NTT R & D, 43 (1994) 1
As shown in 273., etc., the single-crystal epitaxial ferroelectric thin-film optical waveguide does not have surface roughness that causes scattering loss, and damages substrates such as oxides of the same type as the thin-film optical waveguide. It is difficult to selectively etch without imparting the surface. For this reason, there has been no report that a channel optical waveguide having a small loss is produced in an epitaxial ferroelectric thin film optical waveguide.

On the other hand, the present inventors have previously described Japanese Patent Application No.
As No. 42285, after forming an amorphous thin film on the surface of a single crystal substrate, a slab type oxide optical waveguide, or the like,
This amorphous thin film is patterned into a convex shape by etching, and then the patterned amorphous thin film is heated to cause solid phase epitaxial growth, thereby forming a patterned epitaxial oxide thin film optical waveguide. Applied for a method of manufacturing a waveguide element. According to this method, the patterning speed is high and the controllability of etching is good, so that an optical waveguide device having a fine pattern can be efficiently and accurately processed, and an extremely smooth edge with small light loss due to scattering. , A pattern having side walls and a surface can be formed. However, this method still leaves room for improvement in the etching rate.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a metal oxide thin film element having higher productivity and good characteristics, particularly a ferroelectric element. Provided is a method of manufacturing a body thin film element, more specifically, it is possible to efficiently form a fine pattern having good characteristics and to manufacture a wide range of ferroelectric thin film elements with high productivity. It is to provide a method for manufacturing the device, which is capable of:

[0007]

The above object can be attained by providing the following method for manufacturing a metal oxide thin film element. (1) A step of forming an amorphous metal oxide thin film containing lead in excess of a stoichiometric composition as a second layer on the first layer, and a step of etching the amorphous metal oxide thin film And a step of crystallizing the etched amorphous metal oxide thin film by heating.
The present invention provides a second layer of an amorphous metal oxide thin film containing lead in excess of the stoichiometric composition to the etching step, so that the etching rate is high,
The etching rate ratio (etching selectivity) of the second layer to the first layer is large, and the second layer can be sufficiently etched without roughening the first layer. Therefore, it is possible to efficiently form a fine pattern such as a channel optical waveguide and a grating while maintaining good etching controllability. Therefore, a wide range of ferroelectric thin film devices such as various high-performance switching devices, modulation devices, filter devices, and deflection devices can be provided with high productivity by the above manufacturing method. In addition, by the above-described etching method, a good fine pattern can be easily provided on a polycrystalline thin film.
The above manufacturing method can be applied to all electronic devices such as nonvolatile memories and DRAMs.

(2) The method for manufacturing a metal oxide thin film element according to (1), wherein the amorphous metal oxide thin film is an amorphous PLZT-based thin film. (3) The method for producing a metal oxide thin film device according to (1) or (2), wherein the device is a ferroelectric thin film device. (4) The above-mentioned (1) to (3), wherein the formation of the amorphous metal oxide thin film is performed by applying a metal organic compound solution to the first layer, and then performing amorphization by heating. The method for producing a metal oxide thin film element according to any one of the above. (5) The method for manufacturing a metal oxide thin film element according to any one of (1) to (4), wherein the etching is wet etching. (6) The method according to any one of (1) to (5), wherein the wet etching includes use of an aqueous HCl solution.
3. The method for producing a metal oxide thin film element according to item 1.

(7) The amorphous metal oxide thin film
Is from 1 mol% to 3 mol% of the amount of lead corresponding to the stoichiometric composition.
The above-mentioned, which contains an excess of 0 mol% of lead.
The metal oxide thin film according to any one of (1) to (6)
Manufacturing method of membrane element. (8) The first layer is made of at least SrTiO._ThreeIncluding
The method according to any one of the above (1) to (7),
The method for manufacturing a metal oxide thin film element described above. (9) The amorphous metal oxide thin film is composed of Pb_1xLa
_x(Zr_yTi_1y)_{1x / 4}O _ThreeCharacterized by a thin film of
Metal acid according to any one of the above (1) to (8)
A method for producing a compound thin film element. (10) In the crystallization step, amorphous P
b_1xLa_x(Zr_yTi_1y)_{1x / 4}O_ThreeIs a solid phase epitaxy
(1) to (9), characterized in that they are grown
The method for producing a metal oxide thin film element according to any one of the above.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a method for producing a fine pattern such as a channel optical waveguide or an optical waveguide having a grating, the present inventors form a fine pattern by etching an amorphous thin film and then crystallize the amorphous thin film. In the method of obtaining a crystalline or epitaxial thin film on which a fine pattern is formed by crystallization or epitaxial growth, when an amorphous metal oxide thin film containing lead in excess of the stoichiometric composition is etched, the etching rate increases. The etching selectivity with the layer under the amorphous thin film is large and the edge, the side wall and the surface are smooth, and the optical waveguide device having the channel optical waveguide or the grating with small scattering loss can be manufactured with higher productivity. Find out what can be done and complete the present invention. It was.

That is, the present invention relates to a method of manufacturing a metal oxide thin film element, particularly a ferroelectric thin film element, wherein the second layer contains an excess of lead over the stoichiometric composition on the first layer. Forming an amorphous metal oxide thin film to be etched, etching the amorphous metal oxide thin film, and crystallizing the etched amorphous metal oxide thin film by heating. In the manufacturing method of the present invention, when the amorphous metal oxide thin film provided on the first layer is etched, the progress of the etching in the depth direction is the first layer and the second layer of the amorphous metal oxide thin film. Stopping at the interface of the thin film, and in addition to the excessive lead content of the amorphous thin film, the etching rate is further increased, and the etching rate ratio of the amorphous thin film to the underlying first layer Since the (etching selectivity) is large, the second layer can be sufficiently etched without roughening the first layer. When wet etching is adopted as the etching method, the above-mentioned effects are remarkably exhibited.

In the method of the present invention, the above-mentioned first layer is a layer which is hardly subjected to etching or a layer whose etching rate is extremely low, and is, for example, a single crystal such as SrTiO ₃ based on a layer structure of a target element. It means a substrate, a single-crystal or epitaxial slab type oxide optical waveguide, a single-crystal or epitaxial buffer layer, or the like. The amorphous metal oxide thin film is provided, for example, on the single crystal substrate, or on the surface of an epitaxial slab-type oxide optical waveguide provided on the single crystal substrate, or provided on the single crystal substrate. It is formed on an epitaxial oxide buffer layer.

The metal oxide of the present invention, for example, a single bond
Crystalline or epitaxial slab type oxide optical waveguide
, Patterned oxide thin film optical waveguide, buffer
ABO is used as the metal oxide for the layers and cladding layers._Three
Type perovskite ferroelectric or electro-optic material
Eg as tetragonal, trigonal, orthorhombic or pseudo-cubic
BaTiO_Three, PbTiO_Three, Pb_1-xLa_x(Zr_yTi_1-y)_{1-x / 4}O_Three (0 <x <0.
3, 0 <y <1.0, PZT, PLT, PLZT depending on the values of x and y), Pb
(Mg_1/3Nb_2/3) O_Three, KNbO_ThreeSuch as hexagonal or trigonal
For example, LiNbO_Three, LiTaO_ThreeEtc.
And its ferroelectric with Ti diffusion or proton exchange
Body, Sr for tungsten bronze type_xBa_1-xNb _TwoO₆, Pb_xBa
_1-xNb_TwoO₆Besides, Bi_FourTi_ThreeO₁₂, Pb_TwoKNb_FiveO_Fifteen, K_ThreeLi_TwoNb
_FiveO_FifteenAnd their substituted derivatives. Magnetic
Y as an optical material_ThreeAl_FiveO₁₂, Y_ThreeFe_FiveO ₁₂, Y_ThreeGa_FiveO₁₂Such
And optical amplification materials doped with Er, Nd, Pr, etc.
These include, but are not limited to.

In the present invention, the method of forming an amorphous metal oxide thin film containing lead in excess of the stoichiometric composition includes electron beam evaporation, flash evaporation, ion plating, Rf-magnetron sputtering, ion Amorphous with lead content based on normal stoichiometry by vapor deposition method selected from beam sputtering, laser ablation, MBE, CVD, plasma CVD, MOCVD, etc., or wet process such as sol-gel method, MOD method It can be manufactured by a method similar to the method of manufacturing a thin film. For example, when producing an amorphous thin film containing an excess of lead over the stoichiometric composition by a sol-gel method, when preparing a precursor solution for producing an amorphous thin film, the mixing ratio of the raw material organometallic compound is lead. Organic compounds are added in excess of the stoichiometric composition. In the case of a dry process such as sputtering, an amorphous thin film containing lead in excess of the stoichiometric composition is formed, for example, by using a target in which lead exceeds the stoichiometric composition. Lead is preferably 1% to 30% of the stoichiometric composition, more preferably 1%
Suitably a 〜20% excess. 1% of stoichiometric composition
If the amount is less than the above, the etching rate is not sufficiently improved, and if the amount exceeds 30% of the stoichiometry,
Since precipitation of lead oxide may occur on the surface of the amorphous thin film, the above range is preferable. In the present invention, it is preferable to use an amorphous PLZT-based thin film as the amorphous metal oxide thin film. PLZT
Examples of the system thin film include thin films such as PZT, PLT, and PLZT.

Since the method for manufacturing a metal oxide thin film element of the present invention includes an amorphizing step and a crystallization step, the manufacturing method of the present invention includes the sol-gel method and the M
It is preferable to employ a wet process for performing epitaxial growth by a combination of an amorphous process and a crystallization process, such as an OD method. These wet processes consist of a solid phase epitaxial growth method consisting of an amorphization step in which a solution (precursor solution) of a metal organic compound such as a metal alkoxide or an organic metal salt is applied to a substrate and heated, and a crystallization step in which the solution is heated to a higher temperature. In addition to the low equipment cost and good uniformity in the substrate surface as compared with various vapor phase growth methods, the buffer layer, the slab type oxide optical waveguide, the oxide thin film optical waveguide, and the cladding layer The control of the refractive index, which is important for controlling the structure, can be easily and reproducibly realized only by adjusting the composition of the metal organic compound precursor in accordance with the refractive index required for each layer. In addition, a buffer layer, an optical waveguide, and a clad layer having low light propagation loss can be manufactured by the solid phase epitaxial growth method. Further, since the solid phase epitaxial growth by the wet process has an effect of flattening a surface having a step, an optical waveguide element manufactured by a manufacturing method using this method has an extremely flat surface.

Precursor used in the above wet process
Organometallic compounds, as well as various metals, and organic compounds
, Preferably an organic compound having a boiling point of 80 ° C or higher at normal pressure.
Metal alkoxide or metal salt which is a reaction product with a product
More choice but not limited to this. Metal Al
As the organic ligand of the cooxide compound, R₁O- or R_TwoOR
_ThreeSelected from O-₁And R_TwoIs an aliphatic hydrocarbon
Represents a group, R_ThreeIs a divalent fat that may have an ether bond
Represents a group hydrocarbon group). These raw materials are in the specified composition
Desirably alcohol having a boiling point of 80 ° C or higher at normal pressure
, Diketones, ketone acids, alkyl esters,
Selected from xy acids, oxy ketones, and acetic acid
After being reacted with or dissolved in a solvent, the substrate
Is applied. These organometallic compounds undergo hydrolysis.
It is possible to apply after the
To obtain a ferroelectric thin film, it is necessary to avoid hydrolysis.
desirable. In addition, these reaction steps involve dry nitrogen
Quality of thin films obtained in a gas or argon atmosphere
Is more desirable.

The metal alkoxide compound as a precursor is synthesized with an organic metal compound such as a metal carboxylate or alkoxide by distillation or reflux in an organic solvent represented by R ₁ OH or R ₂ OR ₃ OH. As the aliphatic hydrocarbon group of R ₁ and R ₂ is preferably an alkyl group having 1 to 4 carbon atoms, R ₃ is an alkylene group having 2 to 4 carbon atoms, 2 to 4 carbon atoms.
Is preferably a divalent group having 4 to 8 carbon atoms in which the alkylene group is bonded by an ether bond. As the solvent having a boiling point of 80 ° C. or higher, specifically, an alcohol exchange reaction of a metal alkoxide is easy, for example, (CH ₃ ) ₂ CHOH (boiling point 82.3
° C), CH ₃ (C ₂ H ₅ ) CHOH (boiling point 99.5 ° C), (CH ₃ ) ₂ CHCH ₂ OH (boiling point 108 ° C), C ₄ H ₉ OH (boiling point 117.7 ° C), (CH ₃ ) ₂ CHC ₂ H ₄ OH (boiling point 130.5 ° C), CH ₃ OCH ₂ CH ₂ OH (boiling point 124.5 ° C), C ₂ H ₅ OCH ₂ CH
Alcohols such as ₂ OH (boiling point 135 ° C) and C ₄ H ₉ OCH ₂ CH ₂ OH (boiling point 171 ° C) are most desirable, but not limited to these, such as C ₂ H ₅ OH (boiling point 78.3 ° C) Can also be used.

This solution is applied on a first layer such as a single crystal substrate by a method selected from a spin coating method, a dipping method, a spray method, a screen printing method and an ink jet method. These coating steps are preferably performed in a dry nitrogen or argon atmosphere from the viewpoint of the quality of the obtained thin film. Thereafter, if necessary, in an atmosphere containing oxygen as a pretreatment, preferably in oxygen, 0.1 to 1000 ° C /
The substrate is heated at a heating rate of 2 seconds, preferably 1 to 100 ° C./second, and the coating layer is heated at a temperature range of 100 ° C. to 500 ° C., preferably 200 ° C. to 400 ° C. where crystallization does not occur. By decomposing, an amorphous thin film is formed. The amorphous thin film is etched by a method described later to form a pattern.

The metal oxide thin film element manufactured in the present invention has an epitaxial oxide buffer layer, an epitaxial slab type oxide optical waveguide, an epitaxial oxide thin film optical waveguide, an epitaxial oxide clad layer, etc. in its structure. However, these epitaxial oxides, the amorphous thin film formed as described above, further in an atmosphere containing oxygen, preferably in oxygen, 1 ~ 500 ° C. / second High-speed heating, desirably at a rate of 10 to 100 ° C./sec.
It can be formed by solid phase epitaxial growth at a temperature of 0 ° C., preferably 600 ° C. to 900 ° C.
In this epitaxial crystallization, at the above temperature
Heating is performed for 1 second to 24 hours, desirably 10 seconds to 12 hours. As the oxygen atmosphere, it is desirable to use an oxygen atmosphere dried for at least a certain time from the viewpoint of the quality of the obtained epitaxial thin film, but it is also possible to humidify as necessary. In these epitaxial crystallization processes, the thickness of one layer is from 10 nm to 1000 nm,
Desirably, a layer having a desired thickness is formed by performing solid phase epitaxial growth of a ferroelectric thin film layer having a thickness of 10 nm to 200 nm on a single crystal substrate at least once. After each epitaxial growth, cooling is performed at a cooling rate of 0.01 to 100 ° C./sec.

Further, the slab-type oxide optical waveguide can be formed not only by the above method but also by impurity diffusion or ion exchange on the surface of the single crystal substrate. Furthermore, in the above description, an element having a single crystal or epitaxial layer has been described. However, the manufacturing method of the present invention forms a patterned polycrystalline thin film by crystallization following etching of an amorphous thin film. It is also effective as a method. Therefore, the method of the present invention can be applied to all electronic devices such as nonvolatile memories and DRAMs.

Next, the etching in the pattern formation of the present invention will be described. In the present invention, in order to carry out solid phase epitaxial growth of a patterned amorphous thin film, extremely smooth edges, side walls, and surfaces are obtained, and as a result, light loss due to scattering is small.
If the polycrystalline thin film is patterned by a similar method,
Edges, side walls, surfaces, and the like are roughened by irregularities due to random crystal grains, and light loss is increased. In general, after applying a photoresist or an electron beam resist to the surface of the amorphous thin film produced as described above, the amorphous thin film is patterned by a series of steps of exposure, development, etching, and resist peeling.
Etching _{HCl, HNO 3, HF, H} 2 SO 4, H 3 PO 4, C 2 H 2 O 2, N
Wet etching using an aqueous solution such as H ₄ F or a mixed aqueous solution thereof, reactive ion etching using a mixed gas of CCl ₄ , CCl ₂ F ₂ , CHClFCF ₃ or the like, and O ₂ thereof,
Alternatively, dry etching such as ion beam etching is effective. Above all, wet etching with 1% to 36% HCl can efficiently etch amorphous thin films containing lead in excess of the stoichiometric composition, making it possible to etch amorphous thin films easily and accurately in a short time. It is.

In particular, in the case of wet etching, the depth and width of the etching can be independently controlled, so that the optical waveguide can be accurately processed into an ideal shape. That is, the etching in the depth direction is stopped by the first layer under the amorphous thin film, which is hardly etched or has a very low etching rate, such as an epitaxial film, and is terminated. Since the thin film is under-etched or side-etched, the etching width can be controlled by adjusting the etching time.
FIG. 5 is a diagram showing an etching state when wet etching is performed in the present invention.
Reference numeral 2 denotes an epitaxial oxide buffer layer, 2a denotes an amorphous thin film which becomes an epitaxial oxide buffer layer by heating, and 8 denotes a photomask. This figure shows an under-etch or side-etch state where the etching is performed wider than the opening of the mask during wet etching.

FIG. 7 shows a photomask 8 (shown by a dotted line in FIG. 7) in which the acute angle portion 9a of the Y-branch portion of the channel waveguide has a rounded shape and the line width of the linear portion has an opening having a predetermined width. FIG. 7 shows the shape of the portion to be removed by the etching when the wet etching is performed (see the solid line in FIG. 7). As FIG. 7 shows,
Even from a mask having a shape in which the acute angle portion 9a of the Y branch portion is blunted, the acute angle portion 9 in which the opening angle of the intersection of the Y branch channel is an acute angle is obtained, and a channel width wider than the opening line width of the mask is obtained. As a result, a Y-branch channel optical waveguide having an ideal shape can be manufactured. Therefore, the radiation loss at the Y-branch is small, and extremely smooth edges, side walls, and surfaces are obtained, so that light loss due to scattering is small.

In the pattern forming method of the present invention, an amorphous thin film containing lead in excess of the stoichiometric composition is subjected to etching, so that the etching rate is further increased.
And the first layer is a single-crystal substrate, a single-crystal or epitaxial slab-type oxide optical waveguide, since the etching selectivity with the epitaxial buffer layer and the like is large, the etch stop is even easier, the above-mentioned Good controllability of wet etching can be further improved.

Patterning by etching of the present invention,
That is, as a fine pattern such as a channel optical waveguide or an optical waveguide having a grating, linear type, S-shaped,
A channel optical waveguide of a Y-branch type, an X-cross type, or a combination thereof can be used, and any of commonly applied buried, ridge, and rib types can be used. A channel optical waveguide structure in which a projection is provided in an optical waveguide and a channel optical waveguide structure in which a cladding layer is provided after a projection is provided in a thin film optical waveguide can be easily manufactured. Since the width and height or depth of the channel are also based on the lamination of thin films, for example, Mach-Zehnder interference switches,
It is easy to select the optimal value depending on the switching method such as directional coupling switch, total reflection type switch, Bragg reflection type switch or digital type switch, curvature of curved channel waveguide, waveguide material and fabrication process. is there. Further, by providing an offset as needed between the S-shaped channel optical waveguides having different bending directions or between the S-shaped channel optical waveguide and the linear channel optical waveguide, the optical propagation loss can be reduced. it can.

Next, an example of an optical waveguide device manufactured by the manufacturing method of the present invention will be described with reference to the drawings. 1 and 2 can be produced by the production method of the present invention.
FIG. 1 shows an example of an optical waveguide device in which a linear channel optical waveguide is formed, FIG. 1 is a sectional view thereof, and FIG. 2 is a perspective view thereof. In the figure, 1 is a substrate, 2 is an epitaxial buffer layer, 3 is an epitaxial slab-type oxide optical waveguide, 4 is an epitaxial linear channel optical waveguide, 5 is an edge portion of the optical waveguide, and 6
Indicates an incident end. (In the following figure,
Since each layer represented by the same numeral indicates the same thing, the description may be omitted. )

FIGS. 3 and 4 show another example of an optical waveguide device in which a linear channel optical waveguide is formed. FIG. 3 is a sectional view, and FIG. 4 is a perspective view. In the figure, 1 is a substrate, 2 is an epitaxial buffer layer patterned in a concave shape, 3 is a patterned epitaxial slab type oxide optical waveguide, 4 is a channel optical waveguide, 5 is an edge portion thereof, and 6 is an edge portion thereof. Each of the incident ends is shown. In this example, a step of epitaxially growing an oxide buffer layer on the surface of a single crystal substrate in advance, forming an amorphous thin film to be an epitaxial oxide buffer layer by heating, and then performing etching to pattern it into a concave shape. An optical waveguide element manufactured by a method including:

Although not shown, an oxide cladding layer may be provided on the surface of the epitaxial oxide thin film optical waveguide or the surface of the epitaxial slab type oxide optical waveguide. Further, a structure having two or more layers of epitaxial oxide thin film optical waveguides, for example, a structure having two or more combinations of a slab type oxide optical waveguide / oxide thin film optical waveguide / oxide cladding layer is also possible. .

FIG. 6 is a view showing a Y-branch channel optical waveguide. 8 and 9 show an example of an optical waveguide device provided with a grating. FIG. 8 is a perspective view thereof, and FIG. 9 is a sectional view thereof. In the figure, reference numeral 10 denotes a grating. FIG. 10 shows an example of a semiconductor element that can be manufactured by the manufacturing method of the present invention. In the figure, 11 is a Si substrate, and 12 is a SiO substrate.
₂ , 13 a Ti thin film, 14 a Pt thin film (lower electrode), 15 a polycrystalline PZT, and 16 a Pt thin film (upper electrode). Fifteen polycrystalline PZTs are formed by heating amorphous PZT after etching.

As described above, according to the present invention, the surface of the first layer, such as a single crystal substrate, an oxide buffer layer, or a single crystal or epitaxial slab type oxide optical waveguide, has a stoichiometric composition. Excess, preferably 1% to 30%,
More preferably, after forming an amorphous thin film containing an excess of 1% to 20% lead, in order to pattern the amorphous thin film by etching, the effect of the manufacturing method according to Japanese Patent Application No. 11-42285, namely, ,
No roughness is observed on the edges, side walls, and surface of the optical waveguide, and an optical waveguide having small light loss due to scattering is formed.
In addition to the effect that the surface of the manufactured optical waveguide element is extremely flat, the etching rate for the amorphous thin film is further increased, and the etching selectivity between the amorphous thin film and the underlying first layer is large. Therefore, there is an effect that the etch stop is easier and the controllability is good. Further, the method can be applied to both wet etching and dry etching. Therefore, a metal oxide thin film element having good characteristics can be manufactured with high productivity by the above manufacturing method. In addition, the above-mentioned method enables a fine pattern such as a channel optical waveguide or a grating to be provided, and a wide range of optical waveguide elements such as various high-performance switching elements, modulation elements, filter elements, or deflection elements can be manufactured with high productivity. It can be provided by. The present invention also provides a method for easily providing a good pattern on a polycrystalline thin film, and can be used for all electronic devices such as nonvolatile memories and DRAMs.

[0031]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited to these Examples. Example 1 In this example, an optical waveguide device shown in FIGS. 1 and 2 in which a buffer layer 2, a slab type oxide optical waveguide 3, and a linear channel type oxide thin film optical waveguide 4 are sequentially provided on a substrate 1 is shown. The manufacturing method will be described. Substrate 1 has a wavelength of 1.3 μm
SrTiO ₃ (100) single crystal substrate with a refractive index of 2.31 at m
The buffer layer 2 is an epitaxial PZT buffer layer with a refractive index of 2.415 and a thickness of 1200 nm in order to enlarge the mode field diameter. The buffer layer is formed by solid-phase epitaxial growth using application of a metal organic compound solution and heating. It is made. The slab type oxide optical waveguide of No. 3 has a refractive index of 2.479.
This is an epitaxial PZT optical waveguide layer having a thickness of 1370 nm and is manufactured in the same manner as the buffer layer. The channel-type optical waveguide of No. 4 has an amorphous PZT thin film formed by applying and heating a metal organic compound solution containing 3% excess of lead by stoichiometry to a thickness of 230 nm, and then has a line width of 6.5 μm.
Fabricated by wet etching with HCl aqueous solution using a linear photoresist pattern of, followed by heating, a refractive index of 2.474 and a thin film of 230 nm
Is an epitaxial channel type optical waveguide.

Hereinafter, a method of manufacturing the optical waveguide device having the above structure will be described in detail. (1) Formation of buffer layer 2 Pb (CH ₃ COO) ₂ anhydrous lead acetate, zirconium isopropoxide Zr (OiC ₃ H ₇ ) ₄ , and titanium isopropoxide
Using Ti (OiC ₃ H ₇ ) ₄ as a starting material, it was dissolved in 2-methoxyethanol, distilled and refluxed, and finally a Pb concentration of 0.6
A precursor solution for a PZT buffer layer having a refractive index of 2.415 after epitaxial growth of M was obtained. Next, this precursor solution was spin-coated on a SrTiO ₃ (100) single crystal substrate which had been washed, etched and dried. The temperature was raised in an O ₂ atmosphere, maintained at 300 ° C., further maintained at 650 ° C., and then cooled. By repeating this, PZT with a thickness of 1200 nm
The buffer layer 2 was grown by solid phase epitaxial growth.

(2) Formation of Slab-Type Oxide Optical Waveguide 3 PZT whose refractive index after epitaxial growth is 2.477
A precursor solution for an optical waveguide layer was prepared in the same manner, spin-coated on the epitaxial PZT buffer layer prepared in the above (1), heated in an O ₂ atmosphere, kept at 300 ° C., and further heated to 650 ° C. After holding at ℃, it was cooled. By repeating this, a 1370 nm-thick PZT optical waveguide layer 3 was grown by solid phase epitaxial growth. (3) Formation of the channel type optical waveguide 4 Thereafter, the PZT optical waveguide is the same as the precursor solution for the PZT optical waveguide layer of the above (2), except that the stoichiometric composition contains a 3% excess of lead. Spin coating on the epitaxial PZT optical waveguide using the layer precursor solution, raising the temperature in an O ₂ atmosphere, holding at 300 ° C., and then repeating the cooling to give a film thickness of 330 nm An amorphous PZT thin film was formed. Next, a photoresist was spin-coated, pre-baked, exposed, and developed to form a resist pattern having a channel width of 6.5 μm. Subsequently, after post-baking, the amorphous PZT thin film is etched with an 18% HCl aqueous solution, the depth direction is stopped by reaching the epitaxial optical waveguide layer, and the channel width is narrower than the resist pattern due to under-etch. By stopping the etching at a time of 5.0 um, an amorphous channel portion was formed with a height of 330 nm and a width of 5.0 um. Next, this was heated and epitaxially grown to form a channel optical waveguide 4 having a height of 230 nm and a width of 5.0 μm. In this embodiment, the etching rate is about 0.1 μm / min, but a higher etching rate can be obtained by increasing the excess amount of lead in the precursor solution. Furthermore, after removing the resist with a remover, the temperature is raised in an O ₂ atmosphere, and the temperature is maintained at 350 ° C.
The solid-phase epitaxial growth of the channel optical waveguide 4 was performed. The refractive index of the obtained channel optical waveguide was 2.478. The crystallographic relationship of the obtained optical waveguide device is as follows: PZT (100) thin film optical waveguide with a single orientation // PZT (100) buffer layer
// SrTiO ₃ (100) substrate, in-plane orientation PZT [001] Thin-film optical waveguide // PZT [001] buffer layer // SrTiO ₃ [001] substrate structure.

As described above, in the present embodiment, since the depth and width at the time of etching can be controlled independently, the channel optical waveguide formed by solid phase epitaxial growth of an amorphous thin film patterned by etching has a scattering property. Very smooth edges, sidewalls, and surfaces with low light loss due to
0.1 μm or less was easily obtained as unevenness or undulation (see FIG. 1). Therefore, the wavelength 1.3
When the um laser beam is introduced into the incident end face 6 (see FIG. 2), the light propagation loss caused by processing the slab type thin film optical waveguide into a channel type in which the light propagation loss is subtracted is negligible. The channel optical waveguide 4 could be accurately processed into an ideal shape. Furthermore, in this example, the amorphous PZT thin film formed from the metal organic compound solution containing 3% excess of lead by stoichiometry was etched, so that etching could be performed in a short time, and better etching controllability was obtained. Therefore, the channel optical waveguide 4 can be accurately processed into an ideal shape.

Example 2 In this example, a buffer layer 2 having a concave-shaped (having a height of 330 nm and a width of 5.0 μm) linear pattern formed on a substrate 1 as shown in FIGS. A method for manufacturing an optical waveguide device provided with the object optical waveguide 3 and the linear channel type oxide thin film optical waveguide 4 will be described. The substrate of No. 1 is SrTiO ₃ (100) having a refractive index of 2.31 at a wavelength of 1.3 μm.
It is a single crystal substrate, and the buffer layer 2 has a refractive index of 2.415
Is an epitaxial PZT buffer layer having a thickness of 1530 nm (1200 nm + 330 nm), and the slab type oxide optical waveguide 3 is an epitaxial PZT optical waveguide having a thickness of 1700 nm (330 nm + 1370 nm).

(1) First, anhydrous lead acetate Pb (CH ₃ COO) ₂ , zirconium isopropoxide Zr (OiC ₃ H ₇ ) ₄ , and titanium isopropoxide Ti (OiC ₃ H ₇ ) ₄ were used as starting materials. Was dissolved in 2-methoxyethanol, distilled and refluxed, and finally a PZT buffer layer precursor solution having a Pb concentration of 0.6M and a refractive index of 2.415 after epitaxial growth was prepared. Next, this precursor solution was spin-coated on a SrTiO ₃ (100) single crystal substrate which had been washed, etched and dried. The temperature is raised in an O ₂ atmosphere, kept at 350 ° C., further kept at 650 ° C., and then cooled. By repeating this, a PZT buffer layer having a thickness of 1200 nm was grown by solid phase epitaxial growth. Next, a PZT buffer layer precursor solution that is the same as the PZT buffer layer precursor solution and differs only in that it contains a 15% excess of lead from the stoichiometric composition is spun onto the epitaxial PZT buffer layer. Coating was performed, the temperature was raised in an O ₂ atmosphere, the temperature was maintained at 300 ° C., and then the temperature was cooled. By repeating this, 330
An amorphous PZT buffer layer having a thickness of nm was formed. Next, a photoresist was spin-coated, pre-baked, exposed, and developed to form a resist pattern having an opening with a channel width of 3.5 μm. Subsequently, after post-baking, the amorphous PZT thin film is etched with a 25% HCl aqueous solution, the depth direction is stopped by reaching the epitaxial buffer layer, and the channel width is wider than the resist pattern by under-etching. Stopping the etching at the time of 5.0 μm, height 330 nm, width 5.0
A groove having a concave shape of μm was formed. The etching rate in this example was 0.2 um / min.

(2) Next, by heating to 650 ° C., the buffer layer having the concave grooves
Solid phase epitaxial growth of PZT thin films was performed. Further, the surface was spin-coated with a precursor solution for a PZT optical waveguide layer, heated in an O ₂ atmosphere, kept at 350 ° C., kept at 650 ° C., and cooled. By repeating this, a 1370 nm-thick PZT optical waveguide layer was grown by solid phase epitaxial growth. The buffer layer having the concave grooves had a refractive index of 2.415. The crystallographic relationship of the optical waveguide device fabricated in this way is a unidirectional PZT (100) thin film optical waveguide // PZT (100) buffer layer //
SrTiO ₃ (100) substrate, in-plane orientation PZT [001] Thin film optical waveguide /
/ PZT [001] buffer layer // SrTiO ₃ [001] substrate structure obtained. In this embodiment, similarly to the first embodiment, etching can be performed with good controllability, and the channel optical waveguide 4 having extremely smooth edge portions 5, side walls, and surfaces can be accurately processed into an ideal shape. Further, the step due to the concave portion formed in the buffer layer was also flattened, and the optical waveguide device of this example had a flat surface.

Example 3 In this example, a buffer layer in which a Y-branch channel-shaped recess as shown in FIG. 6 was formed on a substrate and an optical waveguide element in which a slab-type oxide optical waveguide was formed were used. The manufacturing method will be described. It has the same configuration as that of the optical waveguide device shown in FIG. 4 except that the concave portion has a Y-branch channel shape.
PLZ with a refractive index of 2.420 after epitaxial growth on a SrTiO ₃ (100) single crystal substrate with a refractive index of 2.31 at a wavelength of 1.3 μm.
In the same manner as above using the precursor solution for the T buffer layer, P
The LZT layer was grown by solid phase epitaxial growth at a thickness of 1400 nm. Next, an amorphous PLZT buffer layer having a thickness of 500 nm was formed using the same precursor solution as that for the PLZT buffer layer but containing a lead in excess of 25% of the stoichiometric composition. Subsequently, as shown by the dotted line in FIG.
Wet etching with a 12% HCl aqueous solution was performed using a photomask 8 having a shape in which the acute angle portion 9a of the Y-branch portion of the channel waveguide was rounded and having an opening having a line width of 3.5 μm in a straight line portion. Thereafter, by heating, a solid phase epitaxial growth of a buffer layer having a concave Y-branch pattern was performed. The refractive index of this buffer layer is 2.432
Met. Next, a slab type PZT with a refractive index of
The optical waveguide layer 3 was grown by solid phase epitaxial growth at a thickness of 2200 nm.

The Y-branch type channel of the obtained optical waveguide device has a channel width of 5 μm which is wider than the opening line width of the mask of 3.5 μm, and the opening angle of the intersection of the Y-branch is 0.5.
It was an acute angle of degrees. According to the process of this embodiment,
Since a channel optical waveguide having an ideally shaped Y-branch acute portion 9 can be manufactured even from a mask having a shape in which the acute-angle portion 9a of the Y-branch portion (see FIG. 7) is blunt, radiation loss at the Y-branch portion is reduced. Light losses due to scattering are small due to the small, very smooth edges, sidewalls and surfaces. Also in this example, the surface of the obtained optical waveguide device was flat.

Embodiment 4 In this embodiment, a method of manufacturing an optical waveguide device in which a grating type coupler is provided at an end of a slab type waveguide as shown in FIG. 8 will be described. FIG. 9 shows a sectional view thereof. On the SrTiO ₃ (100) single crystal substrate 1, a slab type PLZT optical waveguide layer 3 is epitaxially grown at 650 ° C. by Rf sputtering. Next, an amorphous PLZT thin film having a composition similar to that of the epitaxial PLZT optical waveguide and containing 15%
After being formed at room temperature by sputtering, wet etching with an aqueous HCl solution is performed using an electron beam resist having a grating-like pattern. After this etching, solid phase epitaxial growth is performed by heating to 750 ° C., and a slab type PLZT optical waveguide device having a grating 8 on the surface can be manufactured.

Embodiment 5 In this embodiment, a method of manufacturing a semiconductor device having a structure as shown in FIG. 10 will be described. In this embodiment, as shown in FIG. 10, a thermally oxidized SiO ₂ , a Ti thin film, and a Pt thin film are laminated on a Si substrate, and a P containing a 25% excess lead over the stoichiometric composition is formed thereon.
An amorphous PZT layer is formed using a ZT layer precursor solution, and wet etching is performed with a 12% HCl aqueous solution using a photoresist 8 having a 10 μm square pattern. Thereafter, by heating to 700 ° C., a 10 μm square pattern is made polycrystalline PZT. Further, a photoresist having an opening pattern of 9 μm square is formed thereon, Pt is formed by sputtering, and then the resist and P on the resist are formed.
By removing t by lift-off, a semiconductor device having a configuration as shown in FIG. 10 can be manufactured.

[0042]

According to the present invention, since the above structure is adopted, the etching rate with respect to the amorphous thin film as the second layer is high, and the etching selectivity between the amorphous thin film and the first layer thereunder. Is large,
Excessive etching to completely etch the second layer does not roughen the underlying first layer. Therefore, the etch stop is easy, the controllability of etching is good, and a metal oxide thin film element having good characteristics can be manufactured with high productivity. In addition, the above-mentioned method enables a fine pattern such as a channel optical waveguide or a grating to be provided, and a wide range of optical waveguide elements such as various high-performance switching elements, modulation elements, filter elements, or deflection elements can be manufactured with high productivity. It can be provided by. The present invention also provides a method for easily providing a good pattern on a polycrystalline thin film, and can be used for all electronic devices such as nonvolatile memories and DRAMs.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing an example of an optical waveguide device provided with a linear channel optical waveguide.

FIG. 2 is a perspective view of the optical waveguide device of FIG.

FIG. 3 is a schematic cross-sectional view showing another example of the optical waveguide device provided with the linear channel optical waveguide.

FIG. 4 is a perspective view of the optical waveguide device of FIG. 3;

FIG. 5 is a conceptual diagram showing a state where an amorphous buffer layer on an epitaxial buffer layer is etched in the present invention.

FIG. 6 is a diagram showing a Y-branch type channel optical waveguide.

FIG. 7 is a diagram showing a relationship between a mask to be used and channels to be formed in patterning a Y-branch channel optical waveguide.

FIG. 8 is a perspective view showing an optical waveguide element provided with a grating.

FIG. 9 is a schematic cross-sectional view of the optical waveguide device of FIG.

FIG. 10 is a schematic cross-sectional view showing one example of a semiconductor device manufactured by the method of the present invention.

[Explanation of symbols]

1: substrate, 2: buffer layer, 2a: amorphous thin film (buffer layer), 3: slab type optical waveguide, 4: channel optical waveguide, 5: edge portion, 6: incident end, 7: cladding layer, 8: mask , 9: Y branch, 10: grating, 11: Si substrate, 12: SiO ₂ film, 13: Ti thin film, 14: Pt lower electrode, 15: polycrystalline PZT, 16:
Pt upper electrode

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H047 KA05 PA02 PA06 PA24 2H049 AA37 AA44 AA46 5F083 AD11 FR01 JA15 PR05 PR25 PR33

Claims (10)

[Claims] 1. A step of forming an amorphous metal oxide thin film containing lead in excess of a stoichiometric composition as a second layer on a first layer, and etching the amorphous metal oxide thin film. And a step of crystallizing the etched amorphous metal oxide thin film by heating. 2. The method according to claim 1, wherein the amorphous metal oxide thin film is an amorphous PLZT-based thin film. 3. The method according to claim 1, wherein the device is a ferroelectric thin film device. 4. The method according to claim 1, wherein the formation of the amorphous metal oxide thin film is carried out by applying a metal organic compound solution to a first layer, and then by heating to form an amorphous state. 4. The method for producing a metal oxide thin film element according to any one of the above items 3. 5. The method for manufacturing a metal oxide thin film device according to claim 1, wherein the etching is wet etching. 6. The method according to claim 1, wherein the wet etching includes the use of an aqueous HCl solution. 7. The amorphous metal oxide thin film,
7. The metal oxide thin-film element according to claim 1, wherein an excess of 1 mol% to 30 mol% of the lead amount corresponding to the stoichiometric composition is contained. Manufacturing method. 8. The method according to claim 1, wherein the first layer contains at least SrTiO ₃ . 9. The method according to claim 1, wherein the amorphous metal oxide thin film is P
_{b 1x La x (Zr y Ti} 1y) 1x / 4 method for producing a metal oxide thin film element according to any one of claims 1 to 8, characterized in that O ₃ is of a thin film. 10. The crystallization process, either amorphous _{Pb 1x La x (Zr y Ti} 1y) 1x / 4 claim O ₃ is characterized in that it is solid phase epitaxial growth 1 to claim 9 2. The method for producing a metal oxide thin film element according to claim 1.