JP2004269305A - Substrate for forming magnetic garnet single crystal film, its manufacturing method, optical element, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably form a high quality thick magnetic garnet single crystal film free from the generation of a crystal defect or warp, a crack, peeling, or the like, in a high yield by liquid phase epitaxial growth by forming a buffer layer of this invention on a commercially available substrate for forming the magnetic garnet single crystal film. <P>SOLUTION: The substrate 2 for forming the magnetic garnet single crystal film is used for growing the magnetic garnet single crystal film by liquid phase epitaxial growth. The substrate 2 has a base substrate 10 whose lattice constant is different from that of the magnetic garnet single crystal film, and the buffer layer 11 which is formed at least on the crystal growth surface of the base substrate 10 and characterized in that the lattice constant at the face brought into contact with the base substrate 10 is substantially the same as that of the base substrate 10 and the lattice constant at the uppermost face is substantially the same as that of the magnetic garnet single crystal film 12. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention uses a substrate for forming a magnetic garnet single crystal film for liquid phase epitaxial growth of a magnetic garnet single crystal film such as a bismuth-substituted rare earth iron garnet (Bi-RIG) single crystal, a method for manufacturing the same, and this manufacturing method. The present invention relates to a substrate manufactured by the above method, a method of manufacturing a single crystal film for performing crystal growth using the substrate, and a single crystal film and an optical element manufactured by the method.
[0002]
[Prior art]
As a material of an optical element such as a Faraday rotator used for an optical isolator, an optical circulator, an optical magnetic field sensor, or the like, generally, a material obtained by epitaxially growing a magnetic garnet single crystal film on a single crystal substrate is used. As a magnetic garnet single crystal film grown on a substrate, a large Faraday rotation coefficient is desired so as to obtain a required Faraday effect. In addition, in order to form a high-quality single crystal film by epitaxial growth, it is necessary that the difference in lattice constant between the substrate single crystal and the growing single crystal film be as small as possible in the temperature range from the film formation temperature to room temperature. Required.
[0003]
It is known that the Faraday rotation coefficient of a magnetic garnet single crystal film is significantly increased by replacing a part of the rare earth component with bismuth. An increase in the amount of bismuth substitution causes an increase in the lattice constant of the magnetic garnet single crystal film at the same time. Therefore, a larger lattice constant is also required for the substrate material used for film formation, for example, by adding Ca, Zr, Mg, or the like. Gadolinium gallium garnet (GGG) with a large lattice constant is used as a single crystal substrate material (see Patent Document 1).
[0004]
However, when attempting to grow a bismuth-substituted rare earth iron garnet single crystal into a thick film (for example, a film thickness of 200 μm or more) on the GGG single crystal substrate to which Ca, Zr, Mg, etc. are added, during the film formation, The substrate or the single crystal film after film formation tends to be warped or cracked, which lowers the production yield during film formation and processing.
[0005]
In order to solve this problem, the present inventors have set a coefficient of thermal expansion in a plane perpendicular to the crystal orientation <111> extremely close to that of a bismuth-substituted rare earth iron garnet single crystal in a temperature range from room temperature to 850 ° C. A garnet single crystal substrate having a specific composition is proposed (see Patent Document 2). By using this single crystal substrate, it is possible to form a thick bismuth-substituted rare earth iron garnet single crystal film having no crystal defects, warpage, or cracks by liquid phase epitaxial growth.
[0006]
However, the garnet single crystal substrate having this specific composition is unstable with respect to the lead oxide flux used as a deposition solvent when liquid-phase epitaxial growth of a bismuth-substituted rare earth iron garnet (Bi-RIG) single crystal film is performed. The present inventors have found that the yield of obtaining a simple bismuth-substituted rare earth iron garnet single crystal is poor. In particular, it has been found that this tendency is large in a substrate composition containing Nb or Ta.
[0007]
Therefore, the present inventors have developed a substrate in which a buffer layer made of a garnet-based single crystal thin film that is stable against flux is formed on the substrate growing surface of a base substrate made of a garnet-based single crystal that is unstable to flux. And filed earlier (see Patent Document 3).
[0008]
[Patent Document 1] Japanese Patent Publication No. 60-4583 [Patent Document 2] JP-A-10-139596 [Patent Document 3] PCT / JP02 / 06223
[Problems to be solved by the invention]
However, the previously proposed invention presupposes a base substrate having a special composition, and cannot use a magnetic garnet single crystal film forming substrate that is currently commercialized. Currently, there are only a few types of commercialized substrates, among which the maximum value of the lattice constant is 1.25 nm, which is the lattice constant of the magnetic garnet single crystal film when bismuth is maximally substituted. There is about 1.5% mismatch compared to 27 nm.
[0009]
In addition, since the buffer layer in the invention proposed earlier is a single layer of the same material, when the lattice constant of the buffer layer is adjusted to the base substrate, the buffer layer deviates from the lattice constant of the magnetic garnet single crystal film to be subjected to liquid phase epitaxial growth. (Mismatch) occurs. When a mismatch in lattice constant occurs, distortion or the like occurs in the magnetic garnet single crystal film, which may cause a defect. Conversely, if the lattice constant of the buffer layer is matched to the lattice constant of the magnetic garnet single crystal film to be subjected to liquid phase epitaxial growth, a lattice constant mismatch occurs between the buffer layer and the base substrate. It is difficult to form without peeling off.
[0010]
The present invention has been made in view of such a situation, and its object is to produce a thick magnetic garnet single crystal film in which crystal defects, warpage, cracking, peeling, etc. do not occur, with high quality and good yield, by liquid phase epitaxial growth. An object of the present invention is to provide a magnetic garnet single crystal film forming substrate, an optical element, and a method for manufacturing the same, which can be formed stably and at low cost. Another object of the present invention is to form a thick magnetic garnet which does not cause crystal defects, warpage, cracking, peeling, etc. by forming the buffer layer of the present invention on a commercially available substrate for forming a magnetic garnet single crystal film. It is an object of the present invention to form a single crystal film with high quality, high yield, stable liquid crystal epitaxial growth, and low cost.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the magnetic garnet single crystal film forming substrate according to the present invention,
A magnetic garnet single crystal film forming substrate for liquid phase epitaxial growth of a magnetic garnet single crystal film,
A base substrate having a different lattice constant from the magnetic garnet single crystal film;
The lattice constant formed on at least the crystal growth surface of the base substrate and in contact with the base substrate is substantially the same as the lattice constant of the base substrate, and the lattice constant on the outermost surface is the lattice of the magnetic garnet single crystal film. A buffer layer substantially identical to the constant.
[0012]
The method for manufacturing a substrate for forming a magnetic garnet single crystal film according to the present invention includes:
Forming a base substrate;
At least a crystal growth surface of the base substrate, a lattice constant on a surface in contact with the base substrate is substantially the same as a lattice constant of the base substrate, and a lattice constant on the outermost surface is a lattice constant of the magnetic garnet single crystal film. Forming a substantially identical buffer layer.
[0013]
In the present invention, the term “substantially the same” means that the difference in lattice constant is within a range of ± 0.0002 nm.
[0014]
According to the present invention, the buffer layer having the outermost surface whose lattice constant is substantially the same as that of the magnetic garnet single crystal to be formed by liquid phase epitaxial growth is formed on at least the crystal growth surface of the base substrate. For this reason, there is no problem such as a mismatch of the lattice constant between the magnetic garnet single crystal film formed on the buffer layer and the surface of the buffer layer, and liquid phase epitaxial growth can be performed stably. Can be improved.
[0015]
For this reason, in the present invention, a bismuth-substituted rare earth iron garnet single crystal film used for an optical element such as a Faraday rotator is suppressed in the occurrence of crystal defects, warpage, cracking, peeling, and the like, with high quality and high production yield. Liquid phase epitaxial growth can be performed. That is, according to the present invention, a magnetic garnet single crystal film having a relatively large thickness (for example, 200 μm or more) and a large area (for example, 3 inches or more in diameter) can be obtained by liquid phase epitaxial growth.
[0016]
Further, the present invention can easily cope with a case where the bismuth-substituted rare-earth iron garnet single crystal film used in an optical element such as a Faraday rotator has a large bismuth substitution amount to improve optical characteristics. For example, if the bismuth substitution amount in the bismuth-substituted rare earth iron garnet single crystal film is increased, its lattice constant also increases. In the present invention, a commercially available single crystal substrate is used as a base substrate, and the buffer layer of the present invention is formed on the surface of the base substrate. Can be adjusted to As a result, the bismuth-substituted rare earth iron garnet single crystal film can be subjected to liquid phase epitaxial growth with high quality and high production yield while suppressing the occurrence of crystal defects, warpage, cracking, and peeling.
[0017]
The lattice constant of the buffer layer may be changed continuously in the film thickness direction or may be changed stepwise. When changing stepwise, the buffer layer may be composed of a multilayer film. The method of forming the buffer layer with a multilayer film is relatively easy to manufacture.
[0018]
Preferably, the buffer layer is
A first buffer layer formed at least on a crystal growth surface of the base substrate and having a lattice constant substantially equal to a lattice constant of the base substrate on a surface in contact with the base substrate;
A second buffer layer laminated directly or indirectly to the first buffer layer and having a lattice constant at the outermost surface substantially equal to a lattice constant of the magnetic garnet single crystal film.
[0019]
Between the first buffer layer and the second buffer layer, one or more intermediate buffer layers having an intermediate lattice constant between them may be laminated.
[0020]
Alternatively, the buffer layer is
It may have a lattice constant gradient layer whose lattice constant changes in the film thickness direction. That is, the lattice constant of the buffer layer may be continuously changed in the thickness direction.
[0021]
Preferably, the lattice constant of the magnetic garnet single crystal film is in the range of 1.2 to 1.3 nm. A magnetic garnet single crystal film having a large lattice constant generally has excellent optical characteristics.
[0022]
Preferably, the magnetic garnet single crystal film is a bismuth-substituted rare earth iron garnet single crystal film. This bismuth-substituted rare earth iron garnet single crystal film can be suitably used as an optical element such as a Faraday rotator.
[0023]
Preferably, the buffer layer includes a bismuth-substituted rare earth iron garnet single crystal film, and a lattice constant of the buffer layer is controlled by a content of bismuth in the buffer layer. In a bismuth-substituted rare earth iron garnet single crystal film, the lattice constant can be controlled by controlling the bismuth content.
[0024]
Preferably, the base substrate contains Nb or Ta. By including Nb or Ta in the base substrate, it is easy to make the thermal expansion coefficient and / or the lattice constant of the base substrate substantially equal to the lattice constant of the magnetic garnet single crystal film. However, when Nb or Ta is included in the base substrate, the stability to the flux tends to deteriorate.
[0025]
In the present invention, the base substrate may be composed of a magnetic garnet single crystal film that is stable to the flux used for the liquid phase epitaxial growth, or may be composed of an unstable garnet-based single crystal. .
[0026]
The flux is not particularly limited, but is, for example, a flux containing lead oxide and / or bismuth oxide. In the present invention, “unstable with respect to flux” means that the solute component in the flux starts crystallization with the target (base substrate or buffer layer) as a nucleus, that is, the target is in a so-called supersaturated state. This means that at least a part of the constituent material is eluted with respect to the flux and / or that at least a part of the flux component is diffused into the target, thereby inhibiting the liquid phase epitaxial growth of the single crystal film. Further, “stable to flux” means the opposite phenomenon of “unstable to flux”.
[0027]
In the present invention, a magnetic garnet single crystal to be formed by liquid phase epitaxial growth, for example, a bismuth-substituted rare earth iron garnet single crystal, a garnet single crystal substrate of a specific composition having a very close thermal expansion coefficient is selected, and the substrate is flux , Liquid-phase epitaxial growth can be performed stably. This is because a buffer layer is formed on the base substrate.
[0028]
Preferably, the thickness of the buffer layer is 1 to 10000 nm, more preferably 5 to 50 nm, and the thickness of the base substrate is 0.1 to 5 mm, more preferably 0.2 to 2.0 mm. If the thickness of the buffer layer is too small, the effect of the present invention is small, and if the thickness is too large, the cost increases and the epitaxial growth film tends to have an adverse effect such as a crack due to a difference in thermal expansion coefficient. If the thickness of the base substrate is too small, the mechanical strength tends to be insufficient and handling workability tends to be poor. If the thickness is too large, cracks and the like tend to increase.
[0029]
Preferably, the base substrate has a thermal expansion coefficient substantially equal to a thermal expansion coefficient of the magnetic garnet single crystal film. Preferably, in a temperature range of 0 ° C. to 1000 ° C., a coefficient of thermal expansion of the base substrate is in a range of ± 2 × 10 ⁻⁶ / ° C. or less with respect to a coefficient of thermal expansion of the magnetic garnet single crystal film. It is in.
[0030]
By making the coefficient of thermal expansion of the base substrate substantially equal to the coefficient of thermal expansion of the magnetic garnet single crystal film, the film after epitaxial growth may be separated from the substrate, cracked or chipped (hereinafter also referred to as “crack”). Quality can be effectively prevented. This is because when a magnetic garnet single crystal film is formed by epitaxial growth, the temperature rises to near 1000 ° C. and then returns to room temperature. If the thermal expansion coefficient is different, cracks and the like are likely to occur in the epitaxially grown film. Because it becomes.
[0031]
The method for producing a magnetic garnet single crystal film according to the present invention uses a substrate for forming a magnetic garnet single crystal film according to any one of the above, and forms a magnetic garnet by liquid phase epitaxy on at least the crystal growth surface of the buffer layer. A step of growing a single crystal film.
[0032]
The method for producing an optical element according to the present invention includes:
After forming the magnetic garnet single crystal film using the method for manufacturing a magnetic garnet single crystal film described above,
Removing the base substrate and the buffer layer to form an optical element made of the magnetic garnet single crystal film.
The optical element according to the present invention is obtained by this manufacturing method.
[0033]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described based on embodiments shown in the drawings.
1 (A) and 1 (B) are schematic cross-sectional views showing a manufacturing process of a substrate for forming a magnetic garnet single crystal film according to one embodiment of the present invention, and FIG. Schematic sectional view showing a process of forming a single crystal film on a substrate,
FIG. 2 is a schematic diagram of an apparatus for performing crystal growth,
FIG. 3 is a cross-sectional view showing a magnetic garnet single crystal film forming substrate according to another embodiment of the present invention and a single crystal film grown using the same.
[0034]
First Embodiment As shown in FIG. 1B, a magnetic garnet single crystal film forming substrate 2 in this embodiment is formed on a base substrate 10 and a crystal growth surface of the base substrate 10. And a buffer layer 11.
[0035]
The base substrate 10 may be a substrate that is unstable with respect to the lead oxide flux or a stable substrate. As the base substrate 10, a substrate commercially available as a substrate for forming a magnetic garnet single crystal film can also be used.
[0036]
In the present embodiment, the buffer layer 11 is formed of a multilayer film having two or more layers, and has a first buffer layer 30 and a second buffer layer 32. The first buffer layer 30 is formed at least on the crystal growth surface of the base substrate 10, and has a lattice constant substantially the same as the lattice constant of the base substrate 10 in a surface in contact with the base substrate 10. The second base substrate 32 is laminated directly or indirectly on the first buffer layer 30, and the lattice constant at the outermost surface is substantially the same as the lattice constant of the magnetic garnet single crystal film 12.
[0037]
Between the first buffer layer 30 and the second buffer layer 32, one or more intermediate buffer layers having an intermediate lattice constant may be laminated. Alternatively, the buffer layer 11 may be formed of a single-layer film of a lattice constant gradient layer in which the lattice constant changes in the film thickness direction, without being formed of a multilayer film. That is, the lattice constant of the buffer layer 11 may be continuously changed in the thickness direction.
[0038]
On the buffer layer 11 of the substrate 2, a bismuth-substituted rare earth iron garnet single crystal film 12 is liquid-phase epitaxially grown as shown in FIG. Since the base substrate 10 grows the magnetic garnet single crystal film 12 via the buffer layer 11, the base substrate 10 has good lattice matching with the single crystal film 12 and has a coefficient of linear thermal expansion close to that of the single crystal film 12. Although it is preferable to have, it is not particularly limited in the present invention.
[0039]
Base substrate 10 are constituted for example the general formula _M1 x _M2 y _M3 z _{O 12} nonmagnetic garnet single crystal represented by. In this general formula, M1 is a metal selected from, for example, Ca, Sr, Cd and Mn. M1 is stably present with a valence of 2+, can take a coordination number of 8, and preferably has an ionic radius in the range of 0.096 to 0.126 nm in this state. M2 is a metal selected from Nb, Ta and Sb, for example. M2 is stably present with a valence of 5+, can take a coordination number of 6, and preferably has an ionic radius in the range of 0.060 to 0.064 nm in this state. M3 is a metal selected from, for example, Ga, Al, Fe, Ge, Si and V. M3 is stably present with a valence of 3+, 4+ or 5+, can take a coordination number of 4, and preferably has an ionic radius in this range of 0.026 to 0.049 nm. Note that these ionic radii are values of effective ionic radii defined by Shannon (RD Shannon). These M1, M2 and M3 may each be a single metal or a combination of two or more metals.
[0040]
Further, in order to adjust the valence and lattice constant, a part of the metal of M1 is substituted with a metal M4 which can be replaced with Ca or Sr in its composition, if necessary, within a range of less than 50 atomic%. May be. M4 may be, for example, at least one selected from Cd, Mn, K, Na, Li, Pb, Ba, Mg, Fe, Co, a rare earth metal and Bi, preferably having a coordination number of 8. Preferably, there is.
[0041]
In the same manner as in the case of M1, M2 may be partially replaced with a metal M5 which can be replaced with Nb, Ta or Sb in a range of less than 50 atomic%. As M5, for example, at least one selected from Zn, Mg, Mn, Ni, Cu, Cr, Co, Ga, Fe, Al, V, Sc, In, Ti, Zr, Si and Sn, preferably The thing which can take the coordination number 6 is illustrated.
[0042]
The single crystal substrate having such a composition has a thermal expansion coefficient close to that of a bismuth-substituted rare earth iron garnet single crystal to be grown, and has good lattice matching with the single crystal. In particular, in the above general formula, it is preferable that x is a number in the range of 2.98 to 3.02, y is 1.67 to 1.72, and z is a number in the range of 3.15 to 3.21.
[0043]
Thermal expansion coefficient of the base substrate 10 having such a composition is at room temperature to 850 ° C., a 1.02 × ^{10 -5} /℃~1.07×10 ^-5 / ℃ about, bismuth-substituted rare earth iron garnet single crystal We are very close to the same linear thermal expansion coefficient of the temperature range 1.09 × ^{10 -5} /℃~1.16×10 ^-5 / ℃ in the membrane.
[0044]
The thickness of the base substrate 10 is not particularly limited. However, when forming a thick bismuth-substituted rare earth iron garnet single crystal film having a thickness of 200 μm or more, the substrate and the single crystal The thickness is preferably 2 mm or less from the viewpoint that generation of cracks and warpage of the film is suppressed and a single crystal film of good quality is obtained. If the thickness of the base substrate exceeds 1.5 mm, the occurrence of cracks near the interface between the substrate and the single crystal film tends to increase as the thickness increases. Further, if the thickness of the single crystal substrate 10 is too small, the mechanical strength is reduced and the handling property is deteriorated. Therefore, a substrate having a thickness of 0.1 mm or more is preferable.
[0045]
The method of manufacturing the base substrate 10 in the magnetic garnet single crystal film forming substrate of the present invention is not particularly limited, and a method commonly used in manufacturing a conventional GGG single crystal substrate or the like can be employed.
[0046]
For example, first, one or two or more metals selected from among the metal represented by M1, the metal represented by M2, and the metal represented by M3 in the above-described general formula, and M4 used in some cases. A homogeneous molten mixture containing one or more metals selected from the metals shown and M5 is prepared at a predetermined ratio. Next, in this molten mixture, for example, a GGG seed crystal whose major axis direction is <111> is immersed perpendicularly to the liquid surface, and pulled up while slowly rotating to form a polycrystal.
[0047]
Since there are many cracks in this polycrystal, a single crystal portion without cracks is selected from the cracks, and after confirming the crystal orientation, the crystal orientation <111> is again used as a seed crystal in the molten mixture. Is immersed so as to be perpendicular to the liquid surface, and pulled up while rotating slowly to form a single crystal free of cracks. Next, this single crystal is cut to a predetermined thickness perpendicular to the growth direction, and both surfaces are mirror-polished, and then, for example, are etched with hot phosphoric acid or the like to obtain a base substrate 10 shown in FIG. .
[0048]
In this embodiment, as shown in FIG. 1B, the first substrate is formed on the base substrate 10 obtained in this manner by a sputtering method, a CVD method, a pulse laser deposition method, or another thin film deposition technique. The buffer layer 11 including the buffer layer 30 and the second buffer layer is formed. Note that the crystal growth surface of the base substrate 10 is preferably planarized by a polishing process or the like before the formation of the buffer layer 11.
[0049]
When the buffer layer 11 is formed by a sputtering method, the inside of the chamber is kept at 0.1 to 10 Pa, preferably 0.5 to 3 Pa, and the target is supplied with a power source at ^{2 to} 10 W / cm ² . More preferably, an input power of 3 to 6 W / cm ² is applied. By controlling the input power in this range, a good quality buffer layer can be formed.
[0050]
In addition, a sputtering gas in which oxygen (O ₂ ) is contained in an inert gas such as Ar at 35% by volume or less, more preferably 10 to 30% by volume, is introduced into the chamber. With a sputtering gas (atmosphere gas) containing no oxygen, the crystal quality of the buffer layer 11 tends to be deteriorated. If the amount of oxygen is too large, abnormal discharge or the like occurs, and a good quality buffer layer 11 can be obtained. It tends to be difficult.
[0051]
During sputtering, the base substrate 10 may be heated, but need not be heated positively. Note that, even when the base substrate 10 is not heated, the temperature of the substrate 10 rises with time due to the effect of the sputtering process. As a result, the temperature of the substrate 10 is lower than room temperature to less than 600 ° C, preferably, room temperature to 300 ° C. C, particularly preferably from room temperature to 100 ° C.
[0052]
The total thickness of the buffer layer 11 formed on the base substrate 10 by such a sputtering process is preferably in the range of 1 to 10000 nm, more preferably 5 to 50 nm. If the thickness of the buffer layer 11 is too small, the effect of the present invention is small. If the thickness is too large, the cost increases, and the epitaxial growth film tends to have an adverse effect such as a crack due to a difference in thermal expansion coefficient. .
[0053]
As shown in FIG. 1C, a magnetic garnet single crystal film made of a bismuth-substituted rare earth iron garnet single crystal film is formed by a liquid phase epitaxial growth method using the substrate 2 for forming a magnetic garnet single crystal film formed as described above. 12 are formed.
[0054]
The composition of the bismuth-substituted rare earth iron garnet single crystal film constituting the magnetic garnet single crystal film 12, for example, the general formula _{Bi m R 3-m Fe 5} -n M n O 12 ( in the formula R is a rare earth metal At least one kind, M is at least one kind of metal selected from Ga, Al, In, Sc, Si, Ti, Ge and Mg, and m and n are 0 <m <3.0, 0 ≦ n ≦ 1.5).
[0055]
In this general formula, examples of the rare earth metal represented by R include Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and the like. Species may be contained, or two or more kinds may be contained.
[0056]
In this single crystal, a part of the rare earth metal represented by R is substituted with bismuth, and the ratio of the substitution with bismuth is represented by m, and the value of m is 0 <m <3.0. Although it is in the range, especially in the range of 0.5 to 1.5, the coefficient of thermal expansion of the single crystal and the coefficient of linear thermal expansion of the single crystal substrate are very similar, which is advantageous. M is a nonmagnetic metal element that can be substituted for Fe, and is Ga, Al, In, Sc, Si, Ti, Ge, or Mg. These may be contained alone or in combination of two or more. You may. The substitution ratio n of the nonmagnetic metal element with Fe is selected in the range of 0 to 1.5.
[0057]
In order to form a bismuth-substituted rare earth iron garnet single crystal film by liquid phase epitaxial growth, for example, first, (1) bismuth oxide, (2) at least one rare earth metal oxide, and (3) iron oxide , (4) a homogeneous melt containing at least one oxide of at least one metal selected from Ga, Al, In, Sc, Si, Ti, Ge and Mg, which is optionally used, Prepare a mixture. As a solute for deposition, lead oxide is usually used as a main component, but other deposition media such as bismuth oxide may be used. If desired, boron oxide or the like may be contained as a crystal growth improver.
[0058]
Next, by dipping the substrate 2 of the present invention in the molten mixture (the solute flux 22 in the crucible 20 shown in FIG. 2), a single crystal is epitaxially grown from the molten mixture on the surface of the buffer layer 11 in the substrate 2. Thus, the magnetic garnet single crystal film 12 is formed. The temperature of the molten mixture at this time varies depending on the composition of the raw material mixture and the like, but is usually selected in the range of 600 to 1000 ° C. The substrate 2 may be allowed to stand still in the molten mixture for epitaxial growth, or may be epitaxially grown while being appropriately rotated by the rotation shaft 24 shown in FIG. When rotating the substrate 2, the number of rotations is advantageously about 10 to 200 rpm. The film forming speed is usually about 0.08 to 0.8 μm / min. The immersion time varies depending on the film-forming speed, desired film thickness, and the like, and cannot be unconditionally determined, but is usually about 10 to 100 hours.
[0059]
After the completion of the epitaxial growth, the substrate 2 is pulled out of the molten mixture, the attached molten mixture is sufficiently shaken off, and then cooled to room temperature. Next, the substrate is immersed in an aqueous solution of a mineral acid such as dilute nitric acid to remove a solidified melt mixture adhering to the surface of the formed single crystal film, and then washed with water and dried. Thus, the thickness of the magnetic garnet single crystal film 12 formed of the bismuth-substituted rare earth iron garnet single crystal formed on the substrate 2 is usually in the range of 100 to 1000 μm. Further, its thermal expansion coefficient, at room temperature to 850 ° C., is 1.0 × ^{10 -5} /℃~1.2×10 ^-5 / ℃ about.
[0060]
Thus, the crystal structure and composition of the bismuth-substituted rare earth iron garnet single crystal film formed on the substrate 2 can be identified by X-ray diffraction and composition analysis using fluorescent X-ray, respectively. The performance of the single crystal film 12 is such that the substrate 2 (base substrate 10 + buffer layer 11) is removed from the single crystal film 12 by polishing, and thereafter, both surfaces of the single crystal film 12 are polished. The evaluation can be performed by providing a non-reflective film on both surfaces and obtaining a Faraday rotation coefficient, a transmission loss, a temperature characteristic, and the like.
[0061]
Second Embodiment As shown in FIG. 3, in the present embodiment, the buffer layer 11 is continuously formed not only on the bottom surface (crystal growth surface) 10a of the base substrate 10 but also on the entire periphery of the side surface 10b. Formed. Other configurations and operations are the same as those of the first embodiment, and thus detailed description thereof will be omitted.
[0062]
In the present embodiment, the buffer layer 11 includes a bottom buffer layer 11 a formed on the bottom surface 10 a of the base substrate 10 and a side buffer layer (side protection film) 11 b formed on the side surface 10 b of the base substrate 10. .
[0063]
In the present embodiment, the buffer layer 11 is formed not only on the bottom surface 10 a of the base substrate 10 but also on the side surface 10 b of the base substrate 10. Therefore, in the present embodiment, not only the bottom surface 10a but also the side surface 10b of the base substrate 10 is polished, and the film is formed under the condition that the buffer layer 11 is formed on the side surface 10b. For example, when a sputtering method is adopted, the side surface protective film 11b is formed not only on the bottom surface 10a of the base substrate 10 but also on the side surface 10b by setting the film forming pressure to 0.1 to 10 Pa, preferably 1 to 3 Pa. Is done. Alternatively, if the MOCVD method is adopted, the side buffer layer 11b is formed not only on the bottom surface 10a of the base substrate 10 but also on the side surface 10b under general film forming conditions.
[0064]
In the present embodiment, the material of the bottom surface buffer layer 11a formed on the bottom surface 10a of the base substrate 10 and the material of the side surface buffer layer 11b formed on the side surface 10b of the base substrate 10 may be different, but are the same. But it's fine. However, it is preferable that these buffer layers 11a and 11b are formed simultaneously. This can reduce the number of steps for forming the buffer layer 11.
[0065]
The film quality of the side buffer layer 11b may be lower than that of the bottom buffer layer 11a. This is because the side growth film 12b to be formed on the surface of the side buffer layer 11b may be removed in a later step. For example, only the bottom buffer layer 10a may be formed by the sputtering method described in the first embodiment, and the side buffer layer 11b may be formed by employing a chemical solution method such as a sol-gel method. Alternatively, a solution for forming the side buffer layer (side protective film) 11b may be applied using a brush or a spray.
[0066]
In this embodiment, the thickness of the bottom buffer layer 11a and the thickness of the side buffer layer 11b may be the same or different. However, the thickness of these buffer layers 11a and 11b is preferably in the range of 1 to 10000 nm, and more preferably in the range of 5 to 50 nm. If the thickness of these buffer layers 11a and 11b is too thin, the effect of the present invention is small, and if the thickness is too thick, the cost increases and the epitaxial growth film tends to have a bad influence such as a crack due to a difference in thermal expansion coefficient. It is in.
[0067]
Using the magnetic garnet single crystal film forming substrate 2 thus configured, a magnetic garnet single crystal film 12 made of a bismuth-substituted rare earth iron garnet single crystal film is formed by a liquid phase epitaxial growth method. In the present embodiment, not only a single crystal film is formed on the bottom surface of the magnetic garnet single crystal film forming substrate 2, but also a side growth film (not necessarily a single crystal film) 12b is formed on the side surface. You. However, the side growth film 12b formed on the side surface of the substrate 2 generally has lower film quality than the bottom single crystal film 12a formed on the bottom surface, and is removed later.
[0068]
In the present embodiment, when the single crystal film 12 is used as an optical element, the side growth film 12b formed on the side surface of the substrate 2 is removed by polishing or the like, and the single crystal film 12a formed on the bottom surface of the substrate 2 is formed. It is preferable to form the optical element only by using the optical element.
[0069]
In particular, in the present embodiment, the buffer layer 11 is formed not only on the crystal growth surface of the base substrate 10 but also on the side surface of the base substrate that intersects the crystal growth surface, so that the side surface of the base substrate 10 reacts with the flux. Instead, the quality of the magnetic garnet single crystal film 12 is improved, and the production yield is also improved.
[0070]
Note that the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention. For example, in the embodiment shown in FIG. 3, the buffer layer 11 is formed only on the bottom surface 10a and the side surface 10b of the base substrate 10, but in the present invention, the entire peripheral surface of the base substrate 10 including the upper surface 10c of the base substrate 10 is provided. Alternatively, the buffer layer 11 may be formed.
[0071]
【Example】
Hereinafter, the present invention will be described based on more detailed examples, but the present invention is not limited to these examples.
[0072]
Example 1
CaCO ₃ , Nb ₂ O ₅ and Ga ₂ O ₃ are weighed and baked at 1350 ° C. in the atmosphere so that the composition of the melt becomes Ca ₃ Nb _1.7 Ga _3.2 O _12. After confirming the phase, the mixture was charged into an iridium crucible and heated to about 1450 ° C. by high-frequency induction and melted in a mixed gas atmosphere of 98% by volume of nitrogen gas and 2% by volume of oxygen gas. Then, a 5 mm prismatic seed crystal having the above-mentioned composition having a major axis direction of <111> was immersed in the melt perpendicularly to the liquid surface, and this was pulled up at a speed of 3 mm / hour under a rotation of 20 rpm. As a result, a transparent single crystal free of any cracks was obtained.
[0073]
Next, about 1 g of each sample was cut out from the upper and lower portions of the crystal, and quantitative analysis was performed on each component metal element using a fluorescent X-ray analyzer. As a result, both Ca ₃ Nb _1.7 Ga and the lower portion of the crystal were analyzed. It was confirmed to have a composition of _3.2 O ₁₂ (CNGG).
[0074]
The obtained single crystal was cut into a predetermined thickness perpendicular to the growth direction, mirror-polished on both sides, and then etched with hot phosphoric acid to produce a CNGG single crystal substrate (base substrate 10). The coefficient of thermal expansion (α) at room temperature to 850 ° C. of this single crystal substrate was 1.07 × 10 ⁻⁵ / ° C. The thickness of this CNGG single crystal substrate was 0.6 mm.
[0075]
The crystal growth surface of the CNGG single crystal substrate, a pulse laser deposition _method to form a first buffer layer 30 of _{Gd 2.2 Yb 1.7 Ga 4.1 O 12} . _{Specifically,} by irradiating KrF excimer laser in the single crystal targets Gd _2.2 Yb _{1.7 Ga} 4.1 _{O 12} In the irradiated laser density 2.0 J / cm ^2, is held by the substrate temperature 600 ° C. CNGG A Gd _2.2 Yb _1.7 Ga _4.1 O ₁₂ thin film having a thickness of about 20 nm was formed on the bottom surface of the substrate under the conditions of an oxygen partial pressure of 1 Pa and an irradiation time of 5 minutes. This Gd _2. X-ray fluorescence analysis of the ₂ Yb _1.7 Ga _4.1 O ₁₂ thin film confirmed that it had the same composition as the target.
[0076]
Next, a single crystal target of Gd _2.4 Yb _1.7 Ga _3.9 O ₁₂ is used on the surface of the first buffer layer composed of the Gd _2.2 Yb _1.7 Ga _4.1 O ₁₂ thin film. In the same manner as described above, a second buffer layer made of Gd _2.4 Yb _1.7 Ga _3.9 O ₁₂ having a thickness of about 20 nm was formed. The total thickness of the buffer layer composed of the first buffer layer and the second buffer layer was about 40 nm.
[0077]
Using the CNGG substrate with a buffer layer (substrate 2) thus obtained, a bismuth-substituted rare earth iron garnet single crystal film was formed by a liquid phase epitaxial growth method. Specifically, 2.155 g of Ho ₂ O ₃ , 5.501 g of Gd ₂ O _3, and 830.0 g of Bi ₂ O ₃ were put in a platinum crucible, melted at about 1000 ° C., and homogenized by stirring. Thereafter, the temperature was lowered at a rate of 120 ° C./hr to maintain a supersaturated state of 805 ° C. Next, the substrate 2 obtained by the above-described method is immersed in the melt, and while the substrate is rotated at 100 rpm, the single crystal film is subjected to liquid phase epitaxial growth for 40 hours. A bismuth-substituted rare earth iron garnet single crystal film 12 having a thickness of about 350 μm was formed.
[0078]
When the composition of the single crystal film 12 formed on the bottom surface of the substrate 2 was analyzed by the X-ray fluorescence method, it was confirmed that the composition was Bi _1.8 Gd _0.9 Ho _0.3 Fe _5.0 O _12. Was. Further, the X-ray rocking curve half value of the obtained single crystal film was 0.02 degrees, and it was confirmed that the single crystal film was a high quality single crystal film.
[0079]
These results, the surface smooth and dense quality, the _{Bi 1.8 Gd 0.9 Ho 0.3 Fe 5.0} O 12 single crystal film of substantially stoichiometric, to generate cracks and peeling It has been confirmed that epitaxial growth can be performed without any problem.
[0080]
When the lattice constant of this single crystal film and the lattice constant of the second buffer layer made of Gd _2.4 Yb _1.7 Ga _3.9 O ₁₂ were examined, both were 1.26 nm. The constant mismatch was almost 0%. We _also examined the lattice constant of the first buffer layer made of Gd _2.2 Yb _{1.7 Ga} 4.1 _{O 12} thin film, and a lattice constant of the base substrate made of CNGG, in both, be 1.25nm And the mismatch of lattice constant was almost 0%. The measurement of the lattice constant was performed by the X-ray diffraction method.
[0081]
The substrate 2 (the base substrate 10 and the buffer layer 11) is removed from the single crystal film 12 by polishing, and both surfaces of the single crystal film 12 are polished, and both surfaces are made of SiO ₂ or Ta ₂ O _5. The Faraday rotation angle at a wavelength of 1.55 μm, the transmission loss at a Faraday rotation angle of 45 deg, and the temperature characteristics were evaluated with a non-reflective film. The characteristics were -0.067 deg / ° C. In each case, the optical characteristics of the optical isolator were at satisfactory levels.
[0082]
Note that the Faraday rotation angle was obtained by irradiating a polarized laser beam having a wavelength of 1.55 μm to the single crystal film and measuring the angle of the polarization plane of the emitted light. The transmission loss was determined from the difference between the laser light intensity at a wavelength of 1.55 μm transmitted through the single crystal film and the light intensity without the single crystal film. The temperature characteristics were calculated by measuring the rotation angle while changing the temperature of the sample from −40 ° C. to 85 ° C., and calculating from the measured value.
[0083]
Furthermore, the coefficient of thermal expansion (α) at room temperature to 850 ° C. of this single crystal film was 1.10 × 10 ⁻⁵ / ° C. The difference in the coefficient of thermal expansion between the base substrate and the single crystal film was 0.03 × 10 ⁻⁵ / ° C. No crack was observed in the obtained single crystal film.
[0084]
Comparative Example 1
A CNGG single crystal substrate was prepared in the same manner as in Example 1, and a bismuth-substituted rare earth iron garnet single crystal film was formed by the same liquid phase epitaxial growth method as in Example 1 without forming any buffer layer thereon. Formed.
[0085]
It was confirmed that the surface of the substrate after the experiment was considerably etched. In addition, X-ray fluorescence analysis showed that a bismuth-substituted rare earth iron garnet single crystal film was not formed.
[0086]
The embodiments and examples described above all illustrate the present invention by way of example and not by way of limitation, and the present invention can be embodied in various other modified and modified forms.
[0087]
【The invention's effect】
As described above, according to the present invention, a thick magnetic garnet single crystal film in which crystal defects, warpage, cracks, peeling, etc. do not occur, has a high quality, a good yield, and is stable by liquid phase epitaxial growth, A substrate for forming a magnetic garnet single crystal film, an optical element, and a method for manufacturing the same, which can be formed at low cost, can be provided.
[0088]
Further, according to the present invention, by forming the buffer layer of the present invention on a commercially available substrate for forming a magnetic garnet single crystal film, a thick film-shaped magnetic garnet single crystal that does not cause crystal defects, warpage, cracking, peeling, etc. A film can be formed stably at low cost with high quality, high yield, and liquid phase epitaxial growth.
[0089]
Furthermore, in the present invention, the present invention can easily cope with a case where the bismuth-substituted rare-earth iron garnet single crystal film used in an optical element such as a Faraday rotator is increased in the amount of bismuth substitution to improve the optical characteristics. .
[Brief description of the drawings]
FIGS. 1A and 1B are schematic cross-sectional views showing a manufacturing process of a substrate for forming a magnetic garnet single crystal film according to an embodiment of the present invention, and FIG. FIG. 4 is a schematic cross-sectional view showing a process of forming a single crystal film on a substrate for forming a crystal film.
FIG. 2 is a schematic view of an apparatus for performing crystal growth.
FIG. 3 is a cross-sectional view showing a magnetic garnet single crystal film forming substrate according to another embodiment of the present invention and a single crystal film grown using the same.
[Explanation of symbols]
2. Magnetic garnet single crystal film forming substrate 10 Base substrate 10a Bottom surface (crystal growth surface)
10b Side surface 10c Top surface 11 Buffer layer 11a Bottom buffer layer 11b Side buffer layer (side protection film)
12 Single crystal film 12a Bottom single crystal film 12b Side growth film 30 First buffer layer 32 Second buffer layer

Claims (15)

A magnetic garnet single crystal film forming substrate for liquid phase epitaxial growth of a magnetic garnet single crystal film,
A base substrate having a different lattice constant from the magnetic garnet single crystal film;
The lattice constant formed on at least the crystal growth surface of the base substrate and in contact with the base substrate is substantially the same as the lattice constant of the base substrate, and the lattice constant on the outermost surface is the lattice of the magnetic garnet single crystal film. A substrate for forming a magnetic garnet single crystal film, comprising: a buffer layer having substantially the same constant as a constant. The buffer layer,
A first buffer layer formed at least on a crystal growth surface of the base substrate and having a lattice constant substantially equal to a lattice constant of the base substrate on a surface in contact with the base substrate;
2. The magnetic layer according to claim 1, further comprising a second buffer layer directly or indirectly stacked on the first buffer layer, wherein a lattice constant at the outermost surface is substantially the same as a lattice constant of the magnetic garnet single crystal film. Garnet single crystal film forming substrate. The buffer layer,
The substrate for forming a magnetic garnet single crystal film according to claim 1, further comprising a lattice constant gradient layer whose lattice constant changes in a film thickness direction. The magnetic garnet single crystal film forming substrate according to any one of claims 1 to 3, wherein a lattice constant of the magnetic garnet single crystal film is in a range of 1.2 to 1.3 nm. The substrate for forming a magnetic garnet single crystal film according to any one of claims 1 to 4, wherein the magnetic garnet single crystal film is a bismuth-substituted rare earth iron garnet single crystal film. The magnetic garnet single crystal according to any one of claims 1 to 5, wherein the buffer layer includes a bismuth-substituted rare earth iron garnet single crystal film, and a lattice constant of the buffer layer is controlled by a content of bismuth in the buffer layer. Crystal film formation substrate. The substrate for forming a magnetic garnet single crystal film according to any one of claims 1 to 6, wherein the base substrate is made of a garnet-based single crystal that is unstable to a flux used for the liquid phase epitaxial growth. The substrate for forming a magnetic garnet single crystal film according to any one of claims 1 to 7, wherein the buffer layer has a thickness of 1 to 10000 nm. The substrate for forming a magnetic garnet single crystal film according to any one of claims 1 to 8, wherein the base substrate has a thermal expansion coefficient substantially equal to a thermal expansion coefficient of the magnetic garnet single crystal film. . In a temperature range of 0 ° C. to 1000 ° C., the coefficient of thermal expansion of the base substrate is within ± 2 × 10 ⁻⁶ / ° C. or less with respect to the coefficient of thermal expansion of the magnetic garnet single crystal film. The substrate for forming a magnetic garnet single crystal film according to claim 9, wherein: The substrate for forming a magnetic garnet single crystal film according to any one of claims 1 to 10, wherein the flux contains lead oxide and / or bismuth oxide as a main component. A method for producing a substrate for forming a magnetic garnet single crystal film according to any one of claims 1 to 11,
Forming a base substrate;
At least a crystal growth surface of the base substrate, a lattice constant on a surface in contact with the base substrate is substantially the same as a lattice constant of the base substrate, and a lattice constant on the outermost surface is a lattice constant of the magnetic garnet single crystal film. Forming a substantially identical buffer layer. 12. A magnetic method comprising: using the substrate for forming a magnetic garnet single crystal film according to claim 1 to grow a magnetic garnet single crystal film on at least a crystal growth surface of the buffer layer by a liquid phase epitaxial growth method. A method for producing a garnet single crystal film. After forming the magnetic garnet single crystal film using the method of manufacturing a magnetic garnet single crystal film according to claim 13,
Removing the base substrate and the buffer layer, and forming an optical element comprising the magnetic garnet single crystal film,
A method for manufacturing an optical element. An optical element obtained by the method for manufacturing an optical element according to claim 14.

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