JPS597674B2 - Method for manufacturing oxide piezoelectric single crystal - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing an oxide piezoelectric single crystal.

Especially suitable for TV PIF surface wave filters.
The present invention relates to a method for manufacturing oxide piezoelectric single crystals such as iTa03. Biot number H = hR/Ks (R: crystal radius,
It has been reported that for crystals with a large value of thermal conductivity (Ks: thermal conductivity), when a longer and larger crystal is pulled up, the temperature gradient on the crystal side decreases rapidly.

For such crystals, the crucible temperature must be lowered to maintain a constant crystal diameter. There are many such oxides, examples include LiTaO3, LiNb0
There is a third prize.

When growing these crystals, conventionally, after soaking the seed crystal in the melt, the crucible temperature is gradually lowered to gradually increase the crystal diameter to the desired diameter as shown in Figure 1, and then the crucible temperature is further lowered. Crystal 1 with a constant diameter was created by lowering the .

In this case, it is reported that the angle θ of the conical shoulder portion 2 of the crystal 1 is at the 450 position, which results in the least strain and fewer defects such as dislocations, resulting in a high quality crystal. (Joint venture, etc., NCCG-5, B
6■-11 (1973) To obtain crystals that do not normally break, θ
It was made in the range of =30 to 600. P for TV receiver
LiTaO3 exhibits excellent properties as an IF filter
In order to put a single-crystal surface acoustic wave filter into practical use, it is required to reduce the cost.

As one method, it is desired to obtain large-diameter crystals in good yield. Increasing the yield means that when obtaining wafers of the same diameter from round crystal rods, the conical portion 2 at the shoulder of each crystal is completely wasted, so it should be reduced as much as possible. □Growing crystals with a constant crystal diameter without fluctuations is possible. In the conventional method, an automatic diameter control device is used for the diameter 2, but not at all for the diameter 1. When growing large-diameter crystals, the pulling growth rate is about the same as that for small-diameter crystals. Therefore, for large-diameter crystals, it takes a very long time to create the shoulder portion. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing an oxide piezoelectric single crystal, which has been devised in view of the above points, and which grows an oxide piezoelectric single crystal having fewer conical portions. That is, the single crystal is grown so that the width of the growth ridge formed on the (102) plane is 3% or more and 30% or less of the crystal diameter. The optimal example of obtaining this growth ridge is by adjusting the supercooled state temperature. In this specification, the width of the growth ridge is the length in the direction perpendicular to the crystal growth direction, and is also referred to as the thickness. For example, after adjusting the temperature of the melt in the crucible to a temperature suitable for crystal growth, a seed crystal is immersed in the melt and the crystal is pulled up several millimeters to approximately the same size as the seed crystal. At this time, the crystal formation temperature is maintained at a quasi-equilibrium temperature. Thereafter, the output of the oscillator is lowered using a program as shown in FIG. 2, and the temperature inside the crucible is lowered. At this time, the temperature decreases faster than the equilibrium state in which heat conduction from the crystals and seed crystals and heat dissipation by heat radiation are balanced, and the melt in the crucible is brought into a stable supercooled state. In this state, crystal a-different planes appear in characteristic directions as facets. LiTaO3, Li
In a crystal such as NbO3, the crystal growth rate is fastest within the plane, and slowest in the direction normal to the plane, and the (102) and its equivalent planes crystallize. If the degree of supercooling is increased to create an unstable supercooled state, the crystal quality will deteriorate and become dendrite-like or polycrystalline. Therefore, the size of the facet surface, such as the growth ridge, is a barometer of how much the state has become supercooled from the normal state when the thermal equilibrium is balanced. Things that influence this include the temperature gradient of the crystal and melt at the solid-liquid interface, and heat radiation from the crystal, but what can actually be controlled are 1. temperature gradient, 2. heat dissipation, and 3. cooling of the melt. In LiNbO3 and LiTaO3, the supercooled state is a metastable state when the thickness of the growth ridge composed of the {102} plane, that is, the (102) plane and its equivalent plane, is within the range of 3% to 30% of the crystal diameter. Something was discovered. LiN
The formation mechanism of the growth edge of the bO3 type crystal is described in the research and practical application report by Yamada et al., Vol. 7 (1965) 338, and is determined by the direction of the pulled crystal and the angle formed by the interface between the crystal and the melt. Therefore, the appearance of growth ridges is different between the shoulder portion of the crystal and the constant diameter portion. The quality of the crystal produced in this region is very good, and although the shoulder angle θ of the crystal was conventionally supposed to be about 30 or higher, it was found that even with θZO, there were no cracks at all. This state is shown in FIG. This fourth
The figure shows data from an experiment to determine whether or not cracks occur in the crystal obtained when the horizontal axis represents the width 1 of the growth edge relative to the crystal diameter D, and the vertical axis represents the shoulder angle θ. In this diagram, if there is a crack, mark it with an ×; if there is no crack, mark it with an ○
It is indicated by a mark. Therefore, if we use a furnace configuration with a temperature gradient that makes it easy to create such a metastable supercooled state, and create crystals based on the above barometer, we can achieve a stable (θSO)
A high yield of crystals of O) can be produced. Example Crucible 8 made of platinum containing 20-40% rhodium
0m7! A cylindrical crucible with a bottom of 1φ×80mmh×2ml was used.

2000 y of raw material for an oxide piezoelectric material, such as lithium tantalate (LjTaO3), was placed in this crucible and melted by high-frequency heating. The internal configuration of the furnace at this time is shown in FIG. The conditions for creating the LjTaO3 melt are as follows: starting materials Ll2CO3 and Ta2O3 are mixed into Li2O/Ta2O
5 - 0.95 and sintered it was used. In FIG. 3, 1 is a furnace body made of alumina refractory. 2 is an alumina crucible, 3 is an alumina disk, and 4 is a platinum rhodium crucible 5 via bubble alumina.

A heat reflecting plate 6 is installed on the upper part of the crucible 5 so that the melt in the crucible 5 can easily create a metastable supercooled state.
The temperature gradient inside and directly above the melt 7 is made gentle. A high-frequency work coil 8 was provided around the furnace body, and the action of this coil 8 lowered the temperature inside the crucible 5 to about 1700° C. and melted it. Furthermore, after adjusting the temperature to an appropriate temperature for pulling the LlTaO3 single crystal, a seed crystal 9 with a size of, for example, 5 x 5 x 100 mm attached to the tip of a seed crystal holder is placed in the melt 7.
Attach it to the surface and pull it at about 5 mm/h. Pull up the crystal with the same thickness as the seed crystal (about 5 m7!Lφ), and adjust the temperature of the melt in the crucible 5 by heat conduction from the seed crystal and radiant heat from the created crystal. Heat escape through radiation, etc. and create a state close to a well-balanced equilibrium state.

Thereafter, the width of the growth ridge formed on the {102} plane is made to be 3% to 30% of the crystal diameter. For example, by rapidly lowering the temperature inside the crucible 5, the above balance is disrupted, the supercooled state is increased, the quasi-stable supercooled state is created, the crystal diameter is expanded, and a single crystal with fewer conical parts is formed. . At this time, the width of the growth ridge composed of (102) is approximately 5 times the crystal diameter.
% to a quasi-stable supercooled state. When the diameter reaches the desired size under these conditions, the output of the oscillator is increased to raise the temperature inside the crucible 5 as shown in Figure 2, thereby reducing the supercooling state and forming the seed crystal. , heat dissipation by heat conduction and thermal radiation from the created crystal approaches the amount of heat flowing into the solid-liquid interface of the melt to maintain a stable supercooled state close to an equilibrium state.

At this time, the rotation is adjusted so that the solid-liquid interface is approximately parallel to the liquid surface, and then the temperature is gradually lowered to create crystals of a constant diameter. As above, 50m7! Ll
A single crystal of 2SX5O 1 was produced in about 11 hours.

The shoulder part was completed in about 2 hours. The shoulder angle was approximately 5 shoulders and the diameter variation was ±0.5 mu. 50mm same as above
When a single crystal of φ×50 mm 1 is produced by the conventional method with a growth edge thickness of 1% or less, the shoulder angle must be at least about 30 mm or more, or cracks will occur in the crystal and a high quality crystal cannot be obtained.

In this case, since the shoulder had been in the area for about 12 hours, the short-time waves in the angular part could be reduced to 1/6. The thickness of the growth ridge showing the above-mentioned barometer of supercooled state is about 1% in diameter in the normal method, but unless it is at least 3%, crystals of θZOO cannot be produced. Also, if the supercooled state is increased to about 30% or more of the diameter,
There was a tendency for the growth ridge to collapse and cracks to appear. Therefore, the metastable supercooled state that can be created by a shoulderless crystal is 3%
It is about 30%.

Example 2 Crucible, for example, size 70mmφ x 70mmh x 1mmt
A cylindrical platinum crucible with a bottom is used, and a lithium niobate melt is placed in it (lithium carbonate L is used as the starting material).
i2CO3253y and niobium pentoxide 8997 are melted by high frequency heating.

It was prepared so that Ll2O/Nb2O5=0.95. ) The furnace structure was as shown in Figure 3. However, in particular, a reflector plate 6 made of Pt was inserted to soften the temperature gradient so that a supercooled state could easily occur. After adjusting the temperature inside the crucible 5 to a temperature suitable for crystal growth, a seed piece of lithium diobate having a size of 3×3×5011 in the Z-axis direction was fixed to a seed crystal holder and dipped into the melt 7. Pull it up at a pulling speed of 511/h, for example, and it will be about 3m below the seed crystal!
Create a crystal with a diameter of 5m1L in length, and set the temperature of the melt in the crucible to a balance between heat conduction from the seed crystal, heat radiation from the created crystal, heat escape due to radiation, etc., and the amount of heat flowing into the solid-liquid interface. Bring the state close to the equilibrium state. After this {102}
The width after growth formed on the surface is 3% to 30% of the crystal diameter. For example, the temperature inside the crucible 5 is rapidly lowered to disrupt the above-mentioned balance and increase the degree of supercooling, thereby increasing the crystal diameter in a metastable supercooling region to form a smaller conical portion.
At this time, the supercooled state was created such that the thickness of the growth ridge composed of {102} planes, that is, 102 planes and their equivalent planes, was approximately 5% of the diameter of the crystal. In this state, when the diameter reaches close to the desired size, the output of the oscillator is increased using the type shown in Fig. 2 to raise the temperature inside the crucible 5 to reduce the supercooling state and release the seeds. A stable supercooled state is maintained in which the amount of heat flowing into the solid-liquid interface of the melt is close to equilibrium between the crystal, heat dissipation by heat conduction from the created crystal, and heat radiation. At this time, the crystal rotation speed was set to 15 rpm so that the solid-liquid interface was approximately parallel to the liquid surface. after that,
Automatic? Screaming? The temperature is gradually lowered by placing the crystal in a constant diameter. 40m7 as above! Lφ×40m
A 71L1 LiNbO3 single crystal was created in about 10 hours.

The shoulder part was made in one and a half hours, the angle of the conical part (shoulder part) is about 71, and the diameter variation is ±0.5m77! It was hot. If the same 40φ x 401 single crystal as above is produced using the conventional method in a furnace where the thickness of the growth ridge is 1% or less, cracks may occur in the crystal unless the shoulder angle is at least about 30mm. Quality crystals cannot be obtained. In this case, it took approximately 11 hours for the shoulder area, so using the method of the present invention reduced the time required for the shoulder formation area to 1/5. As explained above, according to the method of the present invention, the parts become unnecessary in the product manufacturing process.

The time required to create crystal shoulders is approximately 1/5 of the conventional method,
The time required for crystal growth has been significantly shortened. Furthermore, since the shoulder portion of the crystal that becomes unnecessary in the manufacturing process is almost eliminated, products such as wafers can be obtained from the created crystal itself, resulting in a high yield.

For example, 50m77! For a crystal of φ×50 m1fL1, the raw material can be saved by about 10%. In the above embodiment, LiTaO3 and LiNbO3 were described as single crystal materials, but the object of the present invention is not limited to these, and of course LiTaO3 modified from Li/Ta, LiTaO3 added with impurities, etc. It includes.

Also, it naturally contains LiNbO3 which is a different source of Li/Nb, LiNbO3 which has added impurities, and further contains solid solution L.
This also includes the case of iTa(X)Nb(1-X)03 single crystal. Furthermore, if it belongs to the same crystal system as LiNbO3 or LiTaO3 and exhibits a similar ilmenite crystal structure, similar effects are expected, so these are also included.

In Examples 1 and 2, the shoulders were formed while pulling the crystal, but even if the shoulders were formed while the pulling was stopped and then the crystal was formed, shoulderless crystals were obtained in the same manner as in the examples.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the outer shape and shoulder of a crystal produced by the Jumei method, Fig. 2 is a temperature control and oscillator output change program for explaining an embodiment of the method of the present invention, and Fig. 3 is an illustration of the main part of the crystal. Fig. 4 is an explanatory diagram showing the presence or absence of cracks depending on the shoulder angle of the crystal obtained by the method of the invention and the width of the growth ridge with respect to the crystal diameter. be. 1...Alumina refractory, 2...Alumina crucible, 3゜゜゛゜゛゜Alumina disc, 4゜゜゜''゜゜Valve alumina, 5...Platinum rhodium crucible, 6... ...Heat reflector, 7... Melt, 8
...Work coil, 9... Seed crystal,
10...Crystal.

Claims (1)

[Claims] 1. When growing an oxide piezoelectric single crystal from a melt by the pulling method, the width of the growth ridge formed on the {10@2@} plane is 3% to 30% of the crystal diameter. 1. A method for producing an oxide piezoelectric single crystal, the method comprising growing an oxide piezoelectric single crystal so as to have the following properties. 2. The oxide piezoelectric single crystal according to claim 1, wherein the means for growing the oxide piezoelectric single crystal so that the width of the growth ridge is 3% to 30% of the crystal diameter is growth in a supercooled state. manufacturing method. 3. The method for manufacturing an oxide piezoelectric single crystal according to claim 1, wherein the oxide piezoelectric single crystal is a LiTaO_3 single crystal.