JPH11246296A - Liquid phase epitaxial growth method of rare earth-iron garnet film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the LEP(liquid phase epitaxial growth) method of a RIG (rare earth-iron garnet) film, which enables reduction in concentric-circular cracks in the film and improvement in productivity of the film. SOLUTION: This method comprises: bringing a garnet substrate that is a (GdCa)3 (GaMgZr)5 O12 substrate or Nd3 Ga5 O12 substrate, into contact with the liquid surface of a lead oxide based flux contg. a dissolved rare earth iron garnet component; and growing a rare earth-iron garnet film that has a 250 to 600 μm film thickness and a composition represented by the formula (YbTbBi)3 Fe5 O12 , on the garnet substrate so that correlation of the film thickness (t (μm)) of the rare eath-iron garnet film with the thickness (d (μm)) of the garnet substrate meets the relational expression, 6×10<-6> t<-2> -0.0068 t+3.4023>=d/t>=8×10<-6> t<2> -0.0091t+3.5768.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid phase epitaxial growth method for a rare earth-iron garnet film, and more particularly to a magneto-optical device utilizing the Faraday effect of a magneto-optical element, in particular, an optical isolator used for optical communication and a magnetic field intensity measurement. The present invention relates to a liquid phase epitaxial growth method of a rare earth-iron garnet film used in a photomagnetic field sensor that performs a process.

[0002]

2. Description of the Related Art Magneto-optical devices utilizing the Faraday effect of a magneto-optical element have been energetically developed. Among them, the magnitude of the current flowing in the transmission line or distribution line of the substation, which is an optical isolator that blocks return light to the light source in optical communication, and the power transport route from the power plant to the consumer, Optical magnetic field sensors (optical current sensors) for detecting abnormalities have already entered the practical stage from the research stage, and there is a need for cheaper magneto-optical elements for use in magneto-optical devices including these.

[0003] The above-mentioned magneto-optical element is mainly composed of a rare earth-iron garnet film (hereinafter referred to as RIG film), and is usually grown by a liquid phase epitaxial growth method (hereinafter referred to as LPE method).

[0004] The growth of the RIG film by the LPE method involves the formation of flux components such as lead oxide, bismuth oxide, and boron oxide.
Garnet components such as rare earth oxides and iron oxides (in some cases, oxides of non-magnetic elements are also added) are added to a melt at about 900 ° C. which is melted in a platinum crucible to obtain (GdCa)
₃ (GaMgZr) ₅ O ₁₂ substrate or Nd ₃ Ga ₅ O ₁₂ substrate such contacting a garnet substrate, is performed by epitaxially growing the RIG film on the garnet substrate.

The thickness of the grown RIG film is adjusted by polishing in accordance with the wavelength of light to be used and a desired Faraday rotation angle, and is used for a magneto-optical device.

[0006]

However, when a RIG film is grown on a garnet substrate, the surface of the RIG film is formed as shown in FIG.
Concentric cracks as shown in FIG. The concentric cracks may occur on the entire surface of the wafer, but may also concentrate on the outer peripheral portion of the wafer as shown in FIG. If concentric cracks occur on the entire surface of the wafer, the entire surface of the wafer is defective. However, when cracks are concentrated only on the outer peripheral portion of the wafer, even if the garnet substrate on which the RIG film has been grown has a diameter of 2 inches or 3 inches, the magneto-optical device to be finally processed and used is used. Since the shape is several mm in diameter, a portion without concentric cracks at the center of the wafer can be used as a good product and evaluated. In this case, assuming that the distance from the outer peripheral end to the innermost portion of the concentric cracks in the wafer having the radius r is a, the defect rate is 2a / r- (a / r) ² . Conventionally,
The defect rate due to the concentric cracks was about 40%.

The magneto-optical device using the concentric crack portion of the RIG film has deteriorated characteristics such as insertion loss, so that all the devices become defective. This is RIG
It significantly reduces the mass production of membranes.

The present invention has been made in view of the above circumstances, and the present invention provides a RIG capable of reducing concentric cracks and significantly improving productivity.
An object is to provide an LPE method for growing a film.

[0009]

Means for Solving the Problems Warpage occurs due to the difference in the thermal expansion coefficient between the garnet substrate and the growing RIG film,
It is considered that concentric cracks are generated by the generation of tension on the RIG film surface due to the warpage. Therefore, the relationship between the occurrence of concentric cracks and the substrate thickness of the garnet substrate and the thickness of the RIG film was examined in detail by experiments, and the relationship between the substrate thickness of the garnet substrate and the thickness of the RIG film was kept within a certain range. Thus, it was found that concentric cracks were suppressed.

In order to solve the above problems, the present invention provides a liquid phase epitaxial growth method according to the present invention, in which a garnet substrate is brought into contact with a flux liquid surface in which a rare earth-iron garnet component is dissolved, and a film is formed on the garnet substrate. Thickness 2
A 50 μm to 600 μm RIG film is grown,
When the thickness of the film is t (μm) and the thickness of the garnet substrate is d (μm), the following expression (Equation 3) is satisfied.

[0011]

[Equation 3] 6 × 10 ⁻⁶ t ² −0.0068t + 3.4023 ≧ d / t ≧ 8 × 10 ⁻⁶ t ²
−0.0091t + 3.5768

Further, when the thickness of the RIG film is t (μm) and the thickness of the garnet substrate is d (μm), it is preferable that the following expression (Equation 4) is satisfied.

[0013]

[Equation 4] 7 × 10 ⁻⁶ t ² −0.0082 t + 3.6220 ≧ d / t ≧ 9 × 10 ⁻⁶ t ²
−0.0095t + 3.6437

The above flux is a lead oxide type flux,
The garnet substrate is (GdCa) ₃ (GaMgZr) ₅
In the case of an O ₁₂ substrate or an Nd ₃ Ga ₅ O ₁₂ substrate, the rare earth-iron garnet film is preferably (YbTbBi) ₃ Fe ₅ O ₁₂ .

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors assumed that the garnet substrate had a constant substrate thickness while changing the RIG film thickness.
When a growth experiment of the G film was performed, the distance a (FIGS. 2 and 3) from the outer peripheral end to the innermost portion of the concentric crack tended to increase as the thickness of the RIG film increased. However, it was found that in the case of the RIG film in which the film thickness to be grown is still too small, concentric cracks do not occur, but interface cracks occur at the interface between the garnet substrate and the RIG film.

Therefore, the relationship between the substrate thickness of the garnet substrate and the film thickness of the RIG film, in which the defect rate due to concentric cracks and the defect rate due to interface cracks are both suppressed, was determined.

(GdCa) ₃ (GaM)
In the case of growing a (YbTbBi) ₃ Fe ₅ O ₁₂ film as a RIG film using a gZr) ₅ O ₁₂ substrate or an Nd ₃ Ga ₅ O ₁₂ substrate, the substrate thickness of the garnet substrate and the film thickness of the RIG film were changed. The garnet substrate thickness and the RI that each defective rate is less than 20%
The relationship between the thickness of the G film and the relationship between the thickness of the RIG film and the thickness of the garnet substrate at which the respective defective rates are 5% or less were determined experimentally. A region where any of the defective rates is 20% or less is shown by oblique lines in FIG.

In order to keep the defect rate due to concentric cracks at 20% or less, which is half of the conventional rate, the substrate thickness d (μm) of the garnet substrate and the film thickness t (μm) of the RIG film are expressed by the following equation (1). It has been found that the relationship of Expression 5) should be satisfied.

[0019]

[Equation 5] d / t ≧ 8 × 10 ⁻⁶ t ² −0.0091t + 3.5768 (1)

Further, in order to reduce the defect rate to a small value, for example, 5% or less, the relationship of equation (2) (formula 6) may be used.

[0021]

[Equation 6] d / t ≧ 9 × 10 ⁻⁶ t ² −0.0095t + 3.6437 (2)

Further, in order to keep the defect rate due to interface cracking at 20% or less, the substrate thickness d (μm) of the garnet substrate and R
It was found that the thickness t (μm) of the IG film should be in the relationship of the equation (3) (Equation 7).

[0023]

[Equation 7] d / t ≦ 6 × 10 ⁻⁶ t ² −0.0068t + 3.4023 (3)

Further, in order to reduce the defect rate to a small value, for example, 5% or less, the relationship of equation (4) (Equation 8) may be used.

[0025]

[Equation 8] d / t ≦ 7 × 10 ⁻⁶ t ² −0.0082t + 3.6220 (4)

The above conditions may be because the thermal expansion coefficient of the garnet substrate and the thermal expansion coefficient of the RIG film do not change so much in the commonly used garnet substrate and RIG film, even if the compositions of the garnet substrate and the RIG film are respectively changed. The same condition holds.

In the present invention, the thickness of the RIG film is limited to the range of 250 to 600 μm because the thickness of the general RIG film of the optical isolator for optical communication is 250 to 600 μm.
This is because it is about 00 μm.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An RIG according to the present invention will be described below using examples.
The LPE method for growing a film will be described in more detail.

(Example 1) PbO, B in a platinum crucible
Using i ₂ O ₃ and B ₂ O ₃ as flux, a melt was prepared in which Yb ₂ O ₃ , Tb ₂ O ₃ and Fe ₂ O ₃ were dissolved as RIG components. Then, the melt is heated at 830 ° C. in an electric furnace.
A garnet substrate having a diameter of 2 inches and a substrate thickness of 500 μm is brought into contact with the surface of the melt while heating, and the garnet substrate is rotated at 100 rpm to form a film having a thickness of 45 μm on one surface.
Ten RIG films of 0 μm composition (YbTbBi) ₃ Fe ₅ O ₁₂ were grown.

In the LPE method of this embodiment for growing a RIG film having a thickness of 450 μm on a garnet substrate having a thickness of 500 μm, the conditions of Expressions (1) (5) and (3) are satisfied. Were satisfied, and both the defective rate due to concentric cracks and the defective rate due to interface cracking were within 20%.

(Embodiment 2) The thickness of the garnet substrate is set to 5
The RIG film was set to 10 μm in the same manner as
I raised it.

In the LPE method of this embodiment for growing a RIG film having a thickness of 450 μm on a garnet substrate having a thickness of 550 μm, the conditions of the equations (1) and (3) are satisfied. At the same time, the conditions of Expressions (2) (Equation 6) and (4) Expression (Equation 8) were satisfied, and both the defective rate due to concentric cracks and the defective rate due to interface cracking were extremely good at 5% or less. .

(Embodiment 3) The thickness of the garnet substrate is set to 6
The RIG film was set to 10 μm in the same manner as in Example 1.
I raised it.

In the LPE method of this embodiment for growing a RIG film having a thickness of 450 μm on a garnet substrate having a thickness of 600 μm, the conditions of Expressions (1) and (3) and (3) are satisfied. At the same time, the conditions of Expressions (2) (Equation 6) and (4) Expression (Equation 8) were satisfied, and both the defective rate due to concentric cracks and the defective rate due to interface cracking were extremely good at 5% or less. .

(Embodiment 4) The thickness of the garnet substrate is set to 6
The RIG film was set to 10 μm in the same manner as
I raised it.

In the LPE method of this embodiment for growing a RIG film having a thickness of 450 μm on a garnet substrate having a thickness of 650 μm, the conditions of Expressions (1) and (3) and (3) are satisfied. Were satisfied, and both the defective rate due to concentric cracks and the defective rate due to interface cracking were within 20%.

Comparative Example 1 A garnet substrate having a thickness of 4
80 μm, and the RIG film was
I raised it.

The LPE method of this comparative example, in which a RIG film having a thickness of 450 μm is grown on a garnet substrate having a thickness of 480 μm, does not satisfy the condition of the equation (1) (Equation 5).
In this LPE method, the defect rate due to concentric cracks is 2%.
0% or more.

Comparative Example 2 A garnet substrate having a thickness of 7
The RIG film was set to 10 μm in the same manner as
I raised it.

The LPE method of this comparative example, in which a RIG film having a thickness of 450 μm is grown on a garnet substrate having a thickness of 750 μm, does not satisfy the condition of Expression (3) (Equation 7).
In this LPE method, the failure rate due to interface cracking was 20% or more.

[0041]

As described above, according to the method of the present invention, concentric cracks are reduced and the garnet substrate and the RI
An RIG film with less interfacial cracking at the interface with the G film can be obtained. Therefore, by using the method of the present invention, it is possible to produce the RIG film for the optical isolator and the RIG film for the optical magnetic field sensor at low cost and with high productivity.

[Brief description of the drawings]

FIG. 1 is a relationship diagram showing the relationship between the thickness of a RIG film and the thickness of a garnet substrate / the thickness of a RIG film, in which the percentage of concentric crack defects and the percentage of interface crack defects are within 20%, respectively.

FIG. 2 is a plan view showing one embodiment of an RIG film grown on a garnet substrate.

FIG. 3 is a view taken in the direction of arrows III-III in FIG. 2;

[Explanation of symbols]

 Reference Signs List 1 concentric crack 2 RIG film 3 garnet substrate a distance from outer edge to innermost concentric crack d substrate thickness of garnet substrate t film thickness of RIG film

Claims (3)

[Claims] A garnet substrate is brought into contact with a liquid surface of a flux in which an iron garnet component is dissolved, and a rare earth having a thickness of 250 μm to 600 μm is applied to the garnet substrate.
In the liquid phase epitaxial growth method for growing an iron garnet film, the rare earth-iron garnet film has a thickness of t.
(Μm), and the substrate thickness of the garnet substrate is d (μm).
m), the following equation (Equation 1) is satisfied. [Equation 1] 6 × 10 ⁻⁶ t ² −0.0068t + 3.4023 ≧ d / t ≧ 8 × 10 ⁻⁶ t ²
−0.0091t + 3.5768 2. The film thickness of the rare earth-iron garnet film is t (μ
The liquid-phase epitaxial growth method according to claim 1, wherein the following formula (Equation 2) is satisfied, where m) and the substrate thickness of the garnet substrate is d (μm). [Equation 2] 7 × 10 ⁻⁶ t ² −0.0082 t + 3.6220 ≧ d / t ≧ 9 × 10 ⁻⁶ t ²
−0.0095t + 3.6437 3. The flux is a lead oxide-based flux, and the garnet substrate is (GdCa) ₃ (GaMgZ).
r) ₅ O ₁₂ substrate or Nd ₃ Ga ₅ O ₁₂ substrate, wherein the rare earth-iron garnet film is (YbTbBi) ₃ Fe ₅ O ₁₂
The liquid phase epitaxial growth method according to claim 1, wherein: