JP3201427B2 - Manufacturing method of garnet crystal film - Google Patents

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 garnet crystal film used for an optical device such as an optical isolator or an optical amplifier.

[0002]

_2. Description of the Related Art Conventionally, a garnet crystal film used for an optical device has been grown by dissolving a raw material in a flux (flux) composed of a mixed solution of PbO and B ₂ O ₃ , and having a (111) orientation on the liquid surface. Is performed by a liquid phase epitaxial growth method (LPE) in which a crystal substrate is brought into contact and a uniform crystal is deposited on the substrate. In this case, (1
11) The reason for using a substrate is that it is necessary to match the easy axis of magnetization of the magnetic garnet crystal as the magnetic valve material with the growth direction. This growth method is not only high in technical perfection but also the crystal growth itself. Is commonly used because it is homogeneous.

On the other hand, for example, (100) and (1)
The use of a substrate having a 10) orientation causes the following problems. Therefore, crystal substrates having a orientation other than the (111) orientation have not been generally used so far for crystal growth.

In the prior art, crystal growth has been performed by processing the surface of the substrate crystal as smooth as possible. (1
When a garnet crystal film is subjected to liquid phase epitaxial growth on a substrate of (00) orientation, the (100) orientation is
When the substrate is pulled up from the liquid surface, the adhesive force of the flux is strong, so that crystal growth under different conditions continues to occur, resulting in regions having different film thicknesses and compositions. This is a phenomenon called melt drop, and the area of this portion may reach 1 square centimeter or more, which is a serious obstacle in practical use.

As shown in FIG. 1, when a garnet crystal film is to be grown on the surface of a smooth crystal substrate 1 having a (110) orientation, the crystal growth is projected in a region having a diameter of 2 to 5 mm. Abnormal growth called hillocks occurs in which the raised portions 2 are interspersed. Therefore, (1
10) A uniform crystal cannot be grown on a crystal substrate having an orientation. This is because the growth mechanisms in the film thickness direction and the lateral direction with respect to the crystal orientation (110) become unstable in terms of energy as compared with the (111) orientation.

On the other hand, if the substrate has an orientation slightly deviated from the (110) orientation, crystal growth is possible, but in the case of a magnetic garnet, for example, the axis of easy magnetization is slightly inclined, and birefringence is caused. Cause it. In this case, considering the processing of the crystal film, the symmetry worsens. As a result, the symmetry of the processed shape also worsens.

The (100) or (110) orientation is extremely symmetric since the garnet crystal is cubic , and it is very advantageous if crystal growth is possible in consideration of processing into a device. Nevertheless, there is a problem in crystal growth as described above, and heretofore, it has hardly been used for crystal growth by liquid phase epitaxial growth. Further, regarding other substrate orientations, for example, (2)
Crystal growth was difficult in orientations such as (11), (321), and (210).

[0008]

In the conventional garnet crystal film growth method, it is difficult to grow a uniform crystal film using a crystal substrate other than the (111) orientation as long as the liquid phase epitaxial growth method is used. . An object of the present invention is to solve this problem by processing the substrate such that a crystal plane having an orientation other than the substrate crystal orientation appears on the substrate in advance as a step prior to crystal growth. It is an object of the present invention to provide a method capable of growing a uniform crystal film even on a substrate crystal having no orientation.

In order to achieve such an object, according to the present invention, a homogeneous and high-quality crystal grows on a relatively small area even in a crystal orientation substrate in which crystal growth by liquid phase epitaxial growth is difficult. In fact, or (1
(00) Orientation crystal substrate, even with irregularities (10
0) If a crystal plane other than the orientation is exposed,
In view of the fact that the flux is repelled by the action of the crystal plane other than 0), melt drop cannot be performed.
Processing is performed in advance so that various crystal planes appear on a crystal substrate having an orientation other than (111). On such a substrate surface, not only no melt drop occurs but also so-called hillock growth can be prevented, and a uniform garnet crystal film can be provided.

Regarding the orientation of the substrate crystal, orientations other than (111) and those slightly inclined from them are included in the range of the present invention without any problem. Further, the processing method and the processing shape of the substrate crystal are not limited to the methods described in the embodiments.

[0011]

EXAMPLES Specific examples of the present invention will be described below.

(Embodiment 1) FIGS. 2 to 4 show an example of a garnet crystal manufacturing method according to the present invention.

First, as shown in FIG. 2, a plurality of gadolinium gallium garnet (GGG) substrates 1 having a diameter of 2 inches and a thickness of about 400 μm, which have been mirror-finished in the (110) direction, are provided with a plurality of substrates having a width of 20 μm and a height of 2 μm. Straight ridge 3
, So that the distance from the center to the center between the neighbors is 100 μm,

[0014]

[Outside 1]

[0015] The sides of these ridges 3
It is composed of (001), (112), and (111) planes. A specific method for forming such a ridge 3 is as follows.
For example, it can be easily performed by forming a photoresist mask for forming a ridge on the substrate 1 and then performing etching with hot phosphoric acid.

Next, as shown in FIG. 3, the ridge-processed gadolinium gallium garnet (GGG) substrate 1 is subjected to flux control using PbO and B ₂ O ₃ with yttrium iron garnet controlled to have the same lattice constant. Then, a melt 5 of yttrium iron garnet was prepared and filled in the crucible 6. Using the substrate holder 4, the ridge processing surface of the substrate 1 is brought into contact with the melt 5, and a yttrium iron garnet film 7 having a thickness of about 5 μm is formed on the processing surface by a liquid phase epitaxial growth method as shown in FIG. It was formed to a thickness. The crucible 6 was made of platinum, and the growth temperature was about 900 ° C. The grown yttrium iron garnet film 7 was a homogeneous crystal film.

From the above, according to the present invention,
It was confirmed that a garnet crystal film could be grown in the substrate orientation where crystal growth was difficult.

Example 2 Using the garnet crystal manufacturing method shown in Example 1, a part of yttrium of yttrium iron garnet was changed to bismuth or a rare earth element.
A garnet crystal film in which part or all of iron was replaced with gallium or aluminum was grown to a thickness of about 5 μm on a (110) gadolinium gallium garnet crystal substrate 1 by a liquid phase epitaxial growth method.

At this time, the processing of the substrate was performed in the same pattern as in Example 1, but the direction of the linear ridge was selected to be the (001) direction. The crystal growth was a uniform growth film in the portion where the pattern was formed, as in Example 1.

With respect to these homogeneous growth films, 1.3 to 1.3
When the loss as a slab waveguide with respect to 1.5 μm infrared light was evaluated, the results shown in Table 1 were obtained, and it was confirmed that the crystal film according to the method of the present invention was of sufficiently high quality.

[0021]

[Table 1]

As can be seen from Table 1, the garnet crystal film manufacturing method according to the present invention was able to form various garnet crystal films with sufficiently low loss even on substrate crystals other than the (111) orientation.

A garnet crystal film made of a material obtained by appropriately mixing cerium, praseodymium, neodymium, samarium, europium, terbium, dysprosium, holmium, erbium, thulium, and ytterbium among rare earths is also 0.3 dB. / Cm or less was obtained. It should be noted that loss can be easily estimated to be 0.4 dB / cm or less even in a garnet crystal film in which part of iron is not replaced.

The (110) orientation substrate is considered to be most difficult to grow even in garnet crystal growth using the liquid phase epitaxial growth method (W. VANERK: Jou).
rnal of Crystal Growth 48
P621 (1980)), if it is possible to grow a crystal on a (110) substrate, it can be inferred that it is naturally possible on a substrate of another orientation.

(Example 3) 2 inches in diameter and about 400 in thickness
Using a (100) -oriented gadolinium gallium garnet (GGG) substrate crystal and a yttrium aluminum garnet (YAG) substrate crystal having a smooth surface of μm, the substrate is subjected to the same ridge processing as in Example 1, and thereafter gadolinium gallium. A yttrium gallium garnet (YGG) crystal is formed on a garnet (GGG) substrate, and an yttrium aluminum garnet (YAG) crystal film obtained by substituting a part of yttrium with neodymium is formed on a yttrium aluminum garnet (YAG) substrate. It was grown to a thickness of about 5 μm by a liquid phase epitaxial growth method using a flux composed of B ₂ O ₃ .

At this time, in the gadolinium gallium garnet (GGG) substrate, the direction of the linear pattern is (00)
1) direction, and in the case of an yttrium aluminum garnet (YAG) substrate, the direction was (110).

On the side surfaces of the linear ridge, (010) and (1) for gadolinium gallium garnet (GGG) substrate
Crystal planes such as 20) and (110) appear, and in the yttrium aluminum garnet (YAG) substrate,

[0028]

[Outside 2]

Crystal planes such as those described above appeared.

When the substrate crystal is pulled up from the melt surface,
For both gadolinium gallium garnet (GGG) substrates and yttrium aluminum garnet (YAG) substrates, the flux was well shaken off and no melt drop was observed.

The crystal film grown by the above-mentioned method exhibited a good characteristic that the loss as a slab waveguide was 0.1 dB / cm or less.

In the above configuration, the shape of the ridge formed on the substrate surface is rectangular in cross section. However, the present invention is not limited to this shape, and other shapes such as a triangular cross section and a trapezoidal cross section are also conceivable.

[0033]

As described above, according to the present invention,
In growing a garnet crystal film on a garnet crystal substrate having a crystal orientation that is usually difficult to apply the liquid phase epitaxial growth method, a crystal plane other than the substrate orientation appears on a desired substrate in advance as a pre-process for performing liquid phase epitaxial growth. If such processing is performed, crystal growth becomes easy, and industrial advantages are great.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a substrate showing an example of a garnet crystal growth film according to a conventional manufacturing method.

FIG. 2 is a side sectional view of a gadolinium gallium garnet substrate for explaining an example of a garnet crystal growth control method according to the present invention.

FIG. 3 is a side sectional view for explaining an example of a garnet crystal growth control method according to the present invention, in which a gadolinium gallium garnet substrate is brought into contact with a melt in a crucible.

FIG. 4 is a side sectional view of a gadolinium gallium garnet substrate on which a uniform garnet film is grown on a surface, for explaining an example of a garnet crystal growth control method according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Substrate (for example, gadolinium gallium garnet) 2 Hillock 3 Ridge 4 Substrate holder 5 Melt of PbO / B2 O3 in which raw materials were melted 6 Platinum crucible 7 Crystal film grown on substrate (yttrium iron garnet film)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-80196 (JP, A) (58) Field investigated (Int. Cl. ⁷ , DB name) C30B 1/00-35/00 CA (STN ) JICST file (JOIS) WPI (DIALOG)

Claims (2)

(57) [Claims] 1. A garnet crystal represented by a general formula R ₃ B ₅ O ₁₂ (where R is yttrium, lanthanum, bismuth, and a rare earth element having a valence of 3, and B is any one of iron, gallium, and aluminum) Or a method for producing a garnet crystal film in which a substitutional garnet crystal obtained by replacing some of the constituent elements other than oxygen of the garnet with one or more elements having an equivalent valence is grown on a garnet crystal substrate. The garnet crystal substrate has a crystal orientation of (111) or less.
An outer orientation, in the garnet crystal substrate surface, are allowed to appear crystal plane having an orientation other than the crystal orientation of the substrate,
A method for producing a garnet crystal film, wherein the garnet crystal or the substitutional garnet crystal is grown on the surface. 2. A crystal having an orientation other than the crystal orientation of the substrate on the substrate by artificially forming a ridge on the substrate surface whose side surface has an orientation other than the crystal orientation of the substrate. The method for producing a garnet crystal film according to claim 1, wherein a surface is made to appear.