JP3462258B2 - Manufacturing method of electro-optical products - 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 of manufacturing an electro-optical product.

[0002]

2. Description of the Related Art Lithium niobate (LiNbO ₃ ) single crystal and lithium tantalate (LiTaO ₃ ) single crystal are expected as materials for optoelectronics. It is known to obtain a lithium niobate thin film by a liquid phase epitaxial method on a substrate made of a lithium niobate single crystal or the like. For example, "Appl. Phys. Letters" Vo
According to the description on pages 8 to 10 of l.26 No. 1 (1975), a lithium niobate single crystal thin film is formed on a lithium tantalate single crystal substrate by a liquid phase epitaxial method.
"Mat. Res. Bull" Vol.10 (1975) No. 1373-1
According to the description on page 377, a lithium niobate single crystal thin film is formed on a lithium niobate single crystal substrate by a liquid phase epitaxial method. "J. Appl. Phys." Vo
According to pp. 2536 to 2541 of L.70, No.5, (1991), a lithium niobate single crystal thin film is formed by a liquid phase epitaxial method on a lithium niobate single crystal substrate doped with magnesium oxide. There is.

A film forming method in the liquid phase epitaxial method will be described. First, for example, lithium niobate (solute) and L
Charge and mix with iVO ₃ (melting medium). The saturation temperature corresponding to the composition of the melt charged is T ₀ . The temperature of this melt is maintained at a temperature higher than the saturation temperature T ₀ to uniformly melt lithium niobate and LiVO ₃ . Next, the temperature of the melt is cooled to a temperature lower than the saturation temperature T ₀ to bring the melt into a supercooled state. The substrate is brought into contact with the melt in the supercooled state, and a liquid crystal epitaxial growth of a lithium niobate single crystal film is performed on the surface of the substrate.

[0004]

However, it has been found that the following problems occur in the actual manufacturing process. That is, the production of a single crystal by the liquid phase epitaxial method is known, and the present inventor, for example, forms a YIG (yttrium-iron garnet) single crystal film on the gadolinium-gallium garnet substrate by the liquid phase epitaxial method. I was doing research. In this case, PbO--Bi ₂ O ₃ --B ₂ O ₃ is used as the melting medium of the melt,
The film is formed at about 00 ° C. to form a single crystal film having a thickness of about 100 to 500 μm. Immediately after this film formation, since the thickness of the single crystal film is relatively large, the surface of the single crystal film has irregularities. Of course, when a garnet single crystal film is formed, PbO--Bi ₂ O _3-
A solid phase composed of B ₂ O ₃ is deposited and fixed. However, in the next step, by polishing the surface of the single crystal substrate, the unevenness of the single crystal film is eliminated, and at the same time, the solid phase composed of the melting medium is removed.

However, it has been found that such a method cannot be adopted when the above-mentioned lithium niobate single crystal film or the like is formed by the liquid phase epitaxial method. That is, in the case of producing a lithium niobate single crystal film by the liquid phase epitaxial method, after bringing the lithium niobate single crystal substrate into contact with the melt, the substrate is lifted and pulled out from the melt. It was found that there were a lot of cracks.

An object of the present invention is that when a lithium niobate single crystal film or the like is formed by a liquid phase epitaxial method, cracks are generated in the substrate when the electro-optical single crystal substrate is raised and pulled out from the melt. Is to prevent.

[0007]

The present invention is a method of manufacturing an electro-optical article having an electro-optical single crystal film on an electro-optical single crystal substrate , the method comprising:
By fixing the holder to the plane, the electro-optical single crystal substrate horizontally held by the retainer, the retainer so as not to contact the melt, the liquid in the supercooled state of the melt Under the electro-optic single crystal substrate for the phase
The present invention relates to a method characterized in that the side surfaces are brought into contact with each other and the electro-optic single crystal film is epitaxially grown .
The present invention also provides an electro-optic single crystal on an electro-optic single crystal substrate.
A method of manufacturing an electro-optical product including a crystal film, comprising:
Hold the upper end of the electro-optic single crystal substrate by a holder
Then, suspend this electro-optical single crystal substrate, and
And the holder are not in contact with the melt,
The electro-optic single crystal substrate for the supercooled liquid phase of
Contact and epitaxially grow the electro-optic single crystal film
It relates to a method characterized by:

[0008]

The present inventor has come to the following conclusion as a result of detailed examination of the above-mentioned phenomenon. That is, when the lithium niobate single crystal substrate is brought into contact with the melt and then the substrate is raised and pulled out of the melt, the melt remains on the electro-optic single crystal substrate. This melt did not pose a problem in the case of garnet single crystal, but in the case of a lithium niobate single crystal film or the like, the melt remaining on the substrate is added to the substrate when solidified. It is considered that cracks occur in the substrate due to the stress or the stress caused by the difference in thermal expansion coefficient between the substrate and the molten medium.

The inventor of the present invention has actually examined in detail the residual state of the melt on the substrate, and as a result, the melt remains mainly between the holder or the holder for holding the substrate and the substrate. I understood. Further, in order to remove the melt adhered to the substrate, the present inventor tried to rotate the substrate at a high speed immediately after raising the substrate and pulling it out of the melt, and to shake off the melt by centrifugal force. It was However, even with this method, the melt on the surface of the substrate could be almost removed, but the melt remaining between the substrate and the holder was
It was difficult to completely remove it.

The melt remaining between the substrate and the holder is
In order to remove it by rotating the substrate, it was necessary to rotate the substrate at a very high speed, for example, a high speed exceeding 800 rpm. However, when the substrate is rotated at such a high speed, the substrate is likely to be damaged, which adversely affects the crystallinity of the substrate and the film. In addition to the laboratory level, in order to enable actual mass production, it is necessary to increase the planar size of the substrate, but such a large size substrate can be rotated at high speed so that the center does not move. It is difficult to get it done.

Then, the crack has been generated starting from the contact portion between the substrate and the holder.

Therefore, the present inventor, when holding the electro-optical single crystal substrate by the holder, prevents the holder from coming into contact with the molten material, and the electro-optical single crystal with respect to the liquid phase in the supercooled state. It has been discovered that if the substrates are brought into contact with each other, the melt can be easily removed from the substrate without rotating the electro-optical single crystal substrate at a high speed, and the generation of cracks due to the residual melt can be prevented.

In particular, in the case of garnet etc., cracks due to the residual melt did not occur on the substrate, and in the case of lithium niobate single crystal etc., the reason why the crack due to the residual melt occurred was further examined. I came to the conclusion.

That is, in the case of garnet or the like, the single crystal constituting the substrate is isotropic, but in the case of lithium niobate single crystal or the like, the single crystal constituting the substrate is anisotropic, The crystallinity differs between the thickness direction of the substrate and the plane direction of the substrate. In a substrate having such anisotropy, cracks are likely to occur when the melt remaining on the surface of the substrate solidifies. Therefore, the present invention is particularly suitable for a method of forming an electro-optical single crystal film on an anisotropic electro-optical single crystal substrate by a liquid phase epitaxial method.

Furthermore, according to the present invention, the melt can be shaken off even if the rotation speed of the electro-optic single crystal substrate is reduced. Therefore, damage to the substrate due to rotation is small, and its crystallinity is unlikely to be adversely affected. Further, even if the size of the electro-optical single crystal substrate becomes large, the turning off of the melt by rotation can be easily performed.

[0016]

EXAMPLES In accordance with the present invention, to hold an electro-optic single crystal substrate so that the holder does not contact the melt,
There are the following methods.

(1) The upper end of the electro-optical single crystal substrate is held and the electro-optical single crystal substrate is suspended so that the upper end does not enter the melt. Specifically, it is preferable to provide a through hole in the upper end portion and hold a wire through the through hole. According to this aspect of the present invention, a temperature difference does not occur between the two main surfaces of the electro-optic single crystal substrate, so pyroelectricity due to this temperature difference can be prevented,
It is possible to prevent the cracking of the substrate due to this pyroelectricity.

(2) When the electro-optical single crystal substrate is held horizontally and the lower side surface of the electro-optical single crystal substrate is brought into contact with the liquid phase, the holder does not protrude below the lower side surface. To hold the electro-optic single crystal substrate. In this aspect, there is a method of holding the side surface of the substrate.

(3) In the aspect of (2),
When holding the electro-optical single crystal substrate horizontally, it is preferable to hold the substrate by fixing a holder to the upper side surface of the electro-optical single crystal substrate. According to this method, the substrate can be easily held even when the substrate is thin.

(4) In the aspect of (3),
It is preferable to hold the substrate by bringing the tubular holder into contact with the upper surface of the substrate and sucking the air in the tubular holder. Because holding the substrate and releasing the holding
This is because it is suitable for mass production because it can be easily selected.

The electro-optic single crystal substrate and the electro-optic single crystal film may be made of the same substance, or may be made of different substances. However, both lattice constants must be close. As the electro-optical single crystal, an anisotropic electro-optical single crystal is preferable for the reasons described above.
As an electro-optic single crystal, lithium niobate (LiNb
O ₃ ) single crystal, lithium tantalate (LiTaO ₃ ) single crystal and LiNb _x Ta _1-x O ₃ single crystal (0 <x <1) are preferable.

At present, the electro-optic single crystal substrate is manufactured by the pulling method, and as the lithium niobate single crystal substrate, an optical grade single crystal substrate having good crystallinity has been obtained. However, at the present stage, the crystallinity of the lithium tantalate single crystal substrate manufactured by the pulling method is worse than that of the lithium niobate single crystal substrate. Even if a single crystal film is formed on a lithium tantalate single crystal substrate that is originally poor in crystallinity, a single crystal film having better crystallinity than a film formed on an optical grade lithium niobate single crystal substrate is obtained. Hard to get.

For this reason, at this stage, it is preferable to use an optical grade lithium niobate single crystal as the substrate. However, this problem is a problem with the manufacturing technology by the pulling method, so if an optical grade lithium tantalate single crystal substrate with crystallinity equivalent to that of the lithium niobate single crystal substrate is developed in the future, this will be the substrate. Can be preferably used as.

The solute is lithium niobate or lithium tantalate.
Um and LiNb_xTa _1-xO₃Selected from the group consisting of
In the case of one or more solutes, the melting medium is LiVO
₃And LiBO₂One or more melts selected from the group consisting of
It is preferable to use a melting medium. Between this solute and the melting medium
When a combination is used, the composition of the melt
Is solute 10 mol% -solvent 90 mol% to solute 60 m
ol% -solvent 40 mol% is preferable.

When the proportion of solute is less than 10 mol%, as shown in FIG. 6, for example, in the pseudo-binary phase diagram of solute-melting medium, the slope of the liquidus line becomes too steep,
The change in the concentration of the melt due to film growth becomes large, and it becomes difficult to maintain stable film forming conditions. Solute ratio is 60mo
If it is larger than 1%, the saturation temperature becomes high,
The film forming temperature becomes too high, which makes it difficult to form a single crystal film having good crystallinity.

Further, concrete experimental results will be described. (Experiment 1) A liquid phase epitaxial method was carried out by the holding method schematically shown in FIG. 20 mol% LiNbO
₃ was used melt 2 of ─80mol% LiVO _3. In the crucible 1, the melt 2 was heated to 1000 to 1300 °.
The mixture was stirred at C for 3 hours or more to obtain a sufficiently uniform state, then cooled to 960 ° C and allowed to stand. As the electro-optic single crystal substrate 3, a Z-cut optical grade lithium niobate single crystal substrate 3 having a thickness of 1 mm was used.

A cylindrical holder 4 made of platinum was prepared. An opening 4a is opened at the end of the cylindrical holder 4, and the inside of the cylindrical holder 4 is a cavity 4b. The lower end of the cylindrical holder 4 is brought into contact with the upper side surface 3b of the lithium niobate single crystal substrate 3 and air is sucked in as indicated by an arrow A to remove the lithium niobate single crystal substrate 3 from the substrate 3. It was held horizontally so that the lower side surface 3a faced downward.

In this holding state, the lithium niobate single crystal substrate 3 is rotated at 20 rpm and the descending speed is 1 m.
Approximately 5 m above the liquid surface 2a of the melt 2 as indicated by arrow C at m / min.
It was lowered to m. The substrate 3 was sufficiently preheated so that the temperatures of the lithium niobate single crystal substrate 3 and the melt 2 were in equilibrium.

Next, the temperature of the melt 2 is lowered to 925 ° C. and the melt 2 is supercooled, and then the substrate 3 is set to 5 mm.
The film was formed by bringing the lower surface 3a of the substrate 3 into contact with the liquid surface 2a of the melt 2 while lowering at a descending speed of / min.

After the film formation was completed, the lithium niobate single crystal substrate 3 was separated from the melt 2 as shown by an arrow B at a rising speed of 100 mm / min. Then, the substrate 3 is set to 100 rp
The melt 2 remaining on the substrate 3 was shaken off by rotating at m, 200 rpm, and 500 rpm for 30 seconds. Then, the substrate 3 was slowly cooled to room temperature, and the melt 2 remaining on the surface of the substrate 3 was washed with water and removed.

As a result, 100 rpm, 200 rpm,
No crack was observed on the substrate when the substrate 3 was rotated at any rotation speed of 500 rpm.

The full width at half maximum of the X-ray rocking curve of the lithium niobate single crystal film was measured. Here, the half width of the X-ray rocking curve will be described. The crystallinity of the single crystal substrate and the single crystal film can be evaluated by the half width of the X-ray rocking curve. In general, it can be judged that the smaller the half width is, the better the crystallinity of the single crystal is. This value itself varies depending on the reference crystal or the like used in the X-ray measuring apparatus, and therefore the absolute value cannot be specified.

However, the crystallinity of the single crystal thin film produced by the liquid phase epitaxial method is strongly influenced by the crystallinity of the single crystal substrate. Therefore, in order to judge the crystallinity of the produced single crystal film, the half width of the X-ray rocking curve of the substrate used must be used as a reference. In particular, since an optical grade single crystal substrate is currently produced by the pulling method, it is preferable that the full width at half maximum of the X-ray rocking curve of the single crystal film is smaller than that of the optical grade single crystal substrate.

In practice, the full width at half maximum of the X-ray rocking curve was measured by the double crystal method using reflection on the (001) plane. CuKα1 was used as the incident X-ray, and the (422) plane of GaAs single crystal was used as the monochromator. Further, the X-ray rocking curve of only the lithium niobate single crystal substrate 3 was measured in advance before film formation.

The full width at half maximum of the X-ray rocking curve of the optical-grade lithium niobate single crystal substrate 3 used by the present inventors was 6.8 to 6.9 [arc sec]. It was used as the standard for the crystallinity of the lithium oxide single crystal substrate.

As a result, when the substrate 3 is rotated at a rotation speed of 100 rpm, the half width is 6.4 arc.
sec, the half width is 6.3 arc sec when the substrate 3 is rotated at a rotation speed of 200 rpm, and the half width is 6 when the substrate 3 is rotated at a rotation speed of 500 rpm. It was 0.4 arc sec.

(Experiment 2) Film formation was carried out in the same manner as in Experiment 1 using the method schematically shown in FIG. However,
As the holder 5, a platinum columnar holder 5 is used,
The substrate 3 was held horizontally by adhering the upper side surface 3b to the end surface 5a of the cylindrical holder 5.

After the film formation, the substrate 3 is rotated at 100 rpm for 2
The melt 2 remaining on the substrate 3 was shaken off by rotating each for 30 seconds at 00 rpm and 500 rpm. Then, the substrate 3 was slowly cooled to room temperature, and the melt 2 remaining on the surface of the substrate 3 was washed with water and removed. As a result, 100 rpm,
No cracks were found on the substrate when the substrate 3 was rotated at either 200 rpm or 500 rpm.

The half width of the X-ray rocking curve of the lithium niobate single crystal film was similar to that of Experiment 1.

(Experiment 3) A liquid phase epitaxial method was carried out in the same manner as in FIG. However, the holder 6 as shown in FIG. 3 was used to hold the side surface 3c of the substrate 3.

The main body 6c of the holder 6 has a cylindrical shape, a plurality of elongated arms 6a are joined to the lower end surface 6d of the main body 6c, and bent portions 6b are provided at the tips of the arms 6a. There is. The tip of each bent portion 6b is the side surface 3
It is in contact with c, and the substrate 3 is held horizontally by this portion.

After the film formation, the substrate 3 is set to 100 rpm, 2
The melt 2 remaining on the substrate 3 was shaken off by rotating each for 30 seconds at 00 rpm and 500 rpm. Then, the substrate 3 was slowly cooled to room temperature, and the melt 2 remaining on the surface of the substrate 3 was washed with water and removed. As a result, 100 rpm,
No cracks were found on the substrate when the substrate 3 was rotated at either 200 rpm or 500 rpm.

Also, the half-width of the X-ray rocking curve of the lithium niobate single crystal film was similar to that of Experiment 1.

(Experiment 4) A liquid phase epitaxial method was carried out in the same manner as in FIG. However, the holder 16 as shown in FIG. 4 was used. A main body 16c of the holder 16 has a cylindrical shape, a plurality of elongated arms 16a are joined to the lower end surface of the main body 16c, and a bent portion 16b is provided at the tip of each arm 16a. Each bent portion 16b
Are in contact with the lower edge of the substrate 3, and the tips of the bent portions 16 b are located on the lower side of the substrate 3. As a result, the bent portion 16b is immersed in the melt 2 when the lower surface 3a of the substrate 3 is brought into contact with the melt 2.

After the film formation, the substrate 3 is rotated at 100 rpm for 5
The melt 2 remaining on the substrate 3 was shaken off by rotating at 00 rpm and 800 rpm for 30 seconds. Then, the substrate 3 was slowly cooled to room temperature, and the melt 2 remaining on the surface of the substrate 3 was washed with water and removed. As a result, 100 rpm,
When the substrate 3 was rotated at either rotation speed of 500 rpm or 800 rpm, cracks were found on the substrate.
All of these cracks were generated around the contact portion between the bent portion 16b and the substrate 3.

The half width of the X-ray rocking curve of the lithium niobate single crystal film was measured when the substrate 3 was rotated at 800 rpm. As a result, 7.9ar
The value of c sec was obtained.

(Experiment 5) Film formation was carried out in the same manner as in Experiment 1 using the method schematically shown in FIG. However,
As the holder 20, one having a platinum wire 9 attached to the lower end of a platinum body 8 was used. Further, a through hole 13c is formed in the upper end portion of the lithium niobate single crystal substrate 13.
The wire 9 was passed through the through hole 13c to suspend the substrate 13.

In this holding state, the substrate 13 is lowered at a speed of 1 m.
Approximately 5 m above the liquid surface 2a of the melt 2 as indicated by arrow C at m / min.
It was lowered to m. The substrate 13 was sufficiently preheated so that the temperatures of the substrate 13 and the melt 2 were in equilibrium. Next, the temperature of the melt 2 was lowered to 925 ° C., the melt 2 was brought into a supercooled state, and then the substrate 13 was lowered at a descent rate of 5 mm / min.

At this time, as shown in FIG. 5, the lowering of the substrate 3 was stopped so that the upper end of the substrate 3 was not immersed in the melt 2. In this state, the through hole 13c exists in the non-immersed part 13b and does not exist in the immersed part 13a.

After the film formation, the substrate 13 was pulled up from the melt 2, and then the substrate 13 was slowly cooled to room temperature, and the melt 2 remaining on the surface of the substrate 13 was washed and removed. As a result, no crack was found on the substrate 13.

(Experiment 6) Film formation was carried out in the same manner as in Experiment 5 using the method schematically shown in FIG. However,
When the substrate 13 is dipped in the melt 2, the through holes 23 are present in the dipped portion 22 and not in the non-dipped portion 21. As a result, part of the wire 9 is immersed in the melt 2 when the substrate 13 is brought into contact with the melt 2.

After the film formation, the substrate 13 was pulled up from the melt 2, and then the substrate 13 was slowly cooled to room temperature, and the melt 2 remaining on the surface of the substrate 13 was washed and removed. As a result, cracks were found on the substrate 13, and the cracks were generated around the contact portion between the wire 9 and the substrate 13.

[0053]

According to the present invention, when an electro-optic single crystal film such as a lithium niobate single crystal film is formed on an electro-optic single crystal substrate by a liquid phase epitaxial method,
It is possible to prevent the occurrence of cracks in the substrate at the stage where the electro-optical single crystal substrate is raised and pulled out from the melt.

[Brief description of drawings]

FIG. 1 schematically shows a state in which an upper surface 3b of an electro-optical single crystal substrate 3 is held by a cylindrical holder 4 and a lower surface 3a of the electro-optical single crystal substrate 3 is in contact with a melt 2. It is sectional drawing shown.

FIG. 2 is a schematic diagram showing a state in which an upper surface 3b of an electro-optical single crystal substrate 3 is held by a cylindrical holder 5 and a lower surface 3a of the electro-optical single crystal substrate 3 is in contact with a melt 2. It is sectional drawing shown.

FIG. 3 schematically shows a state in which a side surface 3c of an electro-optical single crystal substrate 3 is held by an arm 6a of a holder 6 and a lower side surface 3a of the electro-optical single crystal substrate 3 is in contact with a melt 2. It is sectional drawing shown.

FIG. 4 is a cross-sectional view schematically showing a state in which an electro-optic single crystal substrate 3 is held by an arm 16a of a holder 16 and a lower surface 3a and a part of the arm 16a are in contact with a melt 2. is there.

FIG. 5 shows a state in which a wire 9 is passed through a through hole 13c at the upper end of the electro-optic single crystal substrate 13, the electro-optic single crystal substrate 13 is hung by the wire 9, and the substrate 13 is in contact with the melt 2. FIG. 3 is a schematic cross-sectional view.

FIG. 6 shows a wire 9 passing through a through hole 23 of an electro-optic single crystal substrate 13 and the electro-optic single crystal substrate 1 is connected by the wire 9.
3 is a cross-sectional view schematically showing a state in which the substrate 3 is suspended and a part of the substrate 13 and the wire 9 is in contact with the melt 2.

[Explanation of symbols]

1 crucible 2 melt 2a melt surface
3, 13 Electro-Optical Single Crystal Substrate 3a Lower Side of Electro-Optical Single Crystal Substrate 3b Upper Side of Electro-Optical Single Crystal Substrate
3c Side surface of electro-optic single crystal substrate 4 Cylindrical holder 5 Cylindrical holder 6, 16, 20 Holder
6a, 16a Arm 6b, 16b Bent part of arm 13a, 22 Immersed part 13b, 21 Non-immersed part 13c, 23
Through hole A Air suction direction B Upward direction C Downward direction

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-7-215799 (JP, A) JP-A-49-15686 (JP, A) JP-A-4-260689 (JP, A) JP-A-5- 186291 (JP, A) JP 5-279178 (JP, A) JP 5-294799 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C30B 1/00-35 / 00 G02F 1/03

Claims (3)

(57) [Claims] 1. A method of manufacturing an electro-optical article comprising an electro-optical single crystal film on an electro-optical single crystal substrate, comprising:
Fix the holder to the upper surface of the electro-optic single crystal substrate
By the horizontally holding the electro-optical single crystal substrate by the holder, this holder is to avoid contact with the melt, wherein the electro-optical single crystal relative to the melt liquid phase in a supercooled state of A method for manufacturing an electro-optical product, which comprises contacting a lower surface of a substrate and epitaxially growing the electro-optical single crystal film. Wherein contacting a tubular retainer on said side surface, holding said electro-optical single crystal substrate by sucking the air in the cylindrical holder, preparation of claim 1, wherein the electro-optical products Method. 3. An electro-optic single crystal film on an electro-optic single crystal substrate.
A method of manufacturing an electro-optical article comprising:
Hold the upper end of the electro-optic single crystal substrate with the holder.
This electro-optic single crystal substrate is hung and the upper end and
Make sure that the holding tool does not come into contact with the melt,
Contact the electro-optic single crystal substrate with the liquid phase in the cooled state
To grow the electro-optic single crystal film epitaxially.
A method for manufacturing an electro-optical product, comprising: