JP2003104797A - Method for forming langasite type single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for effectively forming a uniform langasite type single crystal while preventing a secondary phase from generating. SOLUTION: The method for forming the langasite type single crystal is characterized in that a seed crystal S is placed on the bottom of a crucible 1 for forming the langasite type single crystal, a raw material G is filled thereon, and they are melted in a furnace having temperature gradient in vertical direction, then the langasite type single crystal is formed by moving crucible 1 vertically, wherein both the crucible 1 and the seed crystal have tapers toward downward, and the taper angle of the seed crystal is larger than that of the crucible.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a Langasite type single crystal by the Bridgman method.

[0002]

2. Description of the Related Art Recently, a Langasite type single crystal has a small rate of change in elastic wave propagation velocity and frequency due to temperature, and an electromechanical coupling coefficient (interconversion between electric energy and mechanical energy) that indicates the magnitude of piezoelectricity. Coefficient indicating efficiency)
The surface acoustic wave (Surface Acoustic Wav
Research is being conducted as a substrate material for piezoelectric devices such as e: SAW filters (eg H. Takeda, K. Shimamur).
a, VIChani, T.Fukuda, Effect of starting melt compo
sition on crystal growth of La ₃ Ga ₅ SiO ₁₄ , J.Crystal
Growth 197 (1999) 204. etc.). That is, this Langasite-type single crystal has temperature characteristics equivalent to those of quartz, and has an electromechanical coupling coefficient that is about three times that of quartz, and aims to broaden the band and downsize SAW filters that are widely used in mobile phones and the like. It will be possible. For example, JP-A-10-12620
A surface acoustic wave device using a Langasite type single crystal is described in Japanese Patent Publication No. 9 and the like. The Langasite type single crystal is a single crystal made of a compound represented by the chemical formula La ₃ Ga ₅ SiO ₁₄ .

Conventionally, this Langasite type single crystal has been grown by the Czochralski method. FIG. 4 shows a schematic sectional view of an example of a furnace for performing the Czochralski method. The single crystal growth by this method is performed using the crucible 11, and the heat insulating material 2 of alumina and zirconia is provided outside and above the crucible 11 to form a hot zone. A high-frequency work coil 3 for heating is installed outside the heat insulating material 2. In addition,
A thermocouple 12 is installed at the bottom of the crucible 11. During the growth, the crucible 11 is filled with the fired pellets and heated and melted to obtain a melt L having a predetermined temperature. Then, the Langasite seed crystal S is fixed to the pulling shaft 13,
The Langasite type single crystal C is grown from the melt L at a predetermined rotation speed and pulling rate. The diameter of the Langasite type single crystal C is determined by the weight change signal of the crystal detected by the weight sensor 14 connected to the pulling shaft 13. In the Czochralski method, the shoulder is formed when the crystal is grown from the seed crystal S. However, that portion becomes a useless portion when the ingot is processed into a wafer. In addition, internal stress is generated when forming the shoulder portion, which has been a cause of cracks in the crystal. Further, since necking is formed from a thin seed crystal, if the Langasite-type single crystal C exceeds a certain weight, the weight may not be able to withstand the weight and the necking portion may fall below the necking portion. Therefore, there is a limit to the lengthening of the straight body portion.

Therefore, another method for producing a single crystal has been studied. The Bridgman method is exemplified as another method for producing a single crystal. In the Bridgman method, the seed crystal and the raw material in the crucible are set from the vicinity of the melting point to a position above the melting point, the Langasite type single crystal upper portion and the raw material are melted, and seeding is performed. Then, the crucible is lowered vertically, the temperature gradient formed in the lower part of the furnace is passed, and the langasite-type single crystal is grown by cooling and solidifying the melt, and the langasite corresponding to the orientation of the seed crystal is grown. A mold single crystal is produced. In this Bridgman method, if conditions such as a temperature gradient can be optimized, necking does not occur and shoulders are not formed. Further, by reducing the change in temperature gradient, the thermal strain stress is reduced, and a high quality Langasite type single crystal can be produced. Furthermore, by lengthening the furnace,
A long Langasite type single crystal can be easily produced.

[0005]

By the way, in the conventional Bridgman method, a cylindrical crucible and a seed crystal were used. If the crucible and the seed crystal were cylindrical, it was difficult to bring the crucible and the seed crystal into close contact with each other, so that a gap was created. Then, the melt infiltrated into the gap, and the melt infiltrated was rapidly cooled to form polycrystals. Furthermore, since the crystal grows with this polycrystal as a nucleus to form a secondary phase having an orientation different from that of the seed crystal, the finally obtained Langasite-type single crystal is non-uniform and The quality of the Langasite-type single crystal was low because the formation of phases facilitates the generation of cracks. Further, the seed crystal used for producing the Langasite-type single crystal is repeatedly used, but if the melt penetrates into the gap between the seed crystal and adheres to the seed crystal, it should be cylindrically ground to obtain the diameter. Had to adjust the dimensions of. As a result, the removal operation requires a long time, and as a result, the efficiency of producing the Langasite type single crystal was lowered. The present invention has been made to solve the above problems, and provides a method for producing a langasite type single crystal capable of preventing the formation of a secondary phase and efficiently producing a uniform langasite type single crystal. The purpose is to

[0006]

The method for producing a Langasite type single crystal according to the present invention comprises filling a seed crystal in a lower part of a crucible for growing a Langasite type single crystal and filling a raw material on the seed crystal. Then, after melting the seed crystal and the raw material in a vertical furnace having a temperature gradient in the vertical direction, the Langasite to grow a single crystal by vertically moving the Langasite-type single crystal growing crucible. -Type single crystal, the Langasite-type single crystal growing crucible and the seed crystal have a tapered shape with a diameter decreasing toward the bottom, and the taper angle of the seed crystal is Langasite-type. It is characterized in that it is larger than the taper angle of the crucible for growing a single crystal. Here, the seed crystal is a Langasite-type single crystal seed crystal. The raw material is a raw material for a langasite type single crystal. Further, the taper angle, in the cross-section when the Langasite-type single crystal growth crucible and the seed crystal are cut in the longitudinal direction along the central axis, the extension line of the straight body wall surface and the extension line of the taper wall surface The angle.

As described above, the crucible for growing a Langasite type single crystal and the seed crystal have a tapered shape with a diameter decreasing toward the bottom, and the taper angle of the seed crystal is a Langasite type single crystal growing crystal. If it is larger than the taper angle of the crucible for use, the peripheral portion of the maximum diameter of the seed crystal contacts the inner wall of the tapered portion of the crucible for growing a Langasite type single crystal. When the portion of the circumference of the maximum diameter of the seed crystal contacts the tapered inner wall of the crucible for growing a Langasite type single crystal, the melt does not enter between the crucible for growing a single crystal of Langasite type and the seed crystal, Since no polycrystalline phase is formed, a uniform Langasite type single crystal can be produced. Further, since the polycrystal phase is not formed, the work of cylindrical polishing performed when the seed crystal is repeatedly used can be simplified, and as a result, the efficiency of Langasite type single crystal production is improved. The Langasite-type single crystal produced in this manner is long and of high quality, and is therefore suitable as a material for SAW devices.

In the method for producing a Langasite type single crystal according to the present invention, the seed crystal has a taper angle of 0.5 to 0.5 than a taper angle of the crucible for growing a Langasite type single crystal.
It is preferably larger by 1 °. When the taper angle of the seed crystal is larger than the taper angle of the crucible for growing a Langasite type single crystal by 0.5 to 1 °, the peripheral portion of the maximum diameter of the seed crystal has a taper of the crucible for growing a Langasite type single crystal. In addition to being more easily in contact with the inner wall of the part, the space between the Langasite-type single crystal growing crucible and the seed crystal is narrowed. As a result, it becomes more difficult for the melt to enter, and the formation of a polycrystalline phase can be prevented more effectively.

In the method for producing a Langasite type single crystal of the present invention, it is preferable that the moving speed for vertically moving the Langasite type single crystal growing crucible is 0.3 to 3 mm / hour. The moving speed for vertically moving the crucible for growing the Langasite type single crystal is 0.3 to 3 m.
When it is m / hour, the growing langasite type single crystal can be present in the optimum temperature gradient for crystal growth, so that a more uniform langasite type single crystal can be produced.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a method for producing a Langasite type single crystal of the present invention will be described with reference to FIGS.
FIG. 1 is a sectional view of a furnace used for producing a Langasite type single crystal of the present embodiment. This furnace includes a seed crystal S (referred to as a langasite seed crystal S in this embodiment) and a raw material G.
A platinum single-crystal growing crucible 1 filled with (in this embodiment, referred to as Langasite raw material G), and a heat insulating material 2.
And a high-frequency work coil 3 for heating, and a crucible receiver 5 to which a movable rod 4 is attached.

As shown in FIG. 2, the crucible 1 for growing a Langasite type single crystal has a taper shape in which the diameter becomes smaller toward the bottom in the lower part, and the taper angle is θ ₁
Is. The taper angle θ ₁ is, for example, 1 ° to 45 °. The Langasite type single crystal growing crucible 1 is covered with a platinum foil dust fall prevention lid 7.
At this time, a hard tube 8 may be used to protect the crucible 1 for growing a Langasite type single crystal. Further, the crucible 1 for growing a Langasite type single crystal is placed on a crucible holder 5 in the furnace. A movable rod 4 is attached to the crucible receiver 5. By moving the rod 4 up and down, the Langasite type single crystal growing crucible 1 can be moved up and down in the furnace.

The langasite raw material G in the present invention is produced as follows. First, lanthanum oxide (La
₂ O ₃ ) and gallium oxide (Ga ₂ O ₃ ) and silica (Si
O ₂ ) Are mixed and the mixture is filled in a crucible for raw material preparation, and the crucible for raw material preparation is heated and pre-baked. The temperature at this time is preferably 1100 to 1300 ° C. Due to this temperature range, GaO ₃ becomes GaO _3.
It can be prevented from changing to and evaporating. Then, after cooling the crucible for producing a raw material, the mixture is crushed into a synthetic powder, which is filled in a mold having an inner diameter of the Langasite type single crystal growing crucible 1 or less, and a rubber press is performed by hydrostatic pressure, and then, The pelletized Langasite raw material G is obtained by sintering at 1300 ° C.

The langasite seed crystal S in the present invention is
It has a tapered shape whose diameter decreases toward the bottom.
It The upper surface outer diameter of this Langasite seed crystal S is
It is substantially the same as the inner diameter of the crucible 1 for growing the type single crystal. This
Here, the outer diameter of the upper surface of the Langasite seed crystal S is
The same as the inner diameter of the crucible 1 for growing a single crystal is a langa
The outer diameter of the upper surface of the site seed crystal S is the Langasite type single crystal growth.
It means 99% or more of the inner diameter of the working crucible 1. Also,
The taper angle of the Langasite seed crystal S
Θ₂And θ₂Is for growing Langasite type single crystal
Vessel taper angle θ ₁0.5-1.0 ° larger than
preferable. θ₂Θ₁0.5 to 1.0 ° larger than
As a result, the peripheral portion of the maximum diameter of the Langasite seed crystal S
Is the inner wall of the tapered part of the crucible for growing a Langasite type single crystal
To more easily contact and grow Langasite type single crystal
The space between the crucible 1 and the Langasite seed crystal S is narrow.
Become. As a result, it becomes more difficult for the melt to enter and
It is possible to further prevent the formation of phases.

In the furnace used in the present invention, a temperature gradient capable of vertically growing a Langasite type single crystal C can be provided, and the Langasite type single crystal growing crucible 1 can be moved vertically. If it is possible, there is no particular limitation, and a known furnace can be used. Further, the furnace heating method is not particularly limited as long as a temperature gradient can be provided. As shown in FIG. 3, the temperature of the furnace is increased above the melting point of the Langasite type crystal in the upper part of the furnace, and lowered in the lower part of the furnace to grow the Langasite type single crystal C. The required temperature gradient has been formed. Further, the temperature rising rate of the furnace before the start of the growth of the Langasite seed crystal S is 100 ° C.
/ Hour or less is preferable. Temperature rising rate is 100 ° C
By the following, cracks due to thermal strain of the Langasite seed crystal S can be suppressed.

In producing the Langasite type single crystal C, the Langasite seed crystal S is first filled in the crucible 1 for growing a Langasite type single crystal in such a direction that the surface of the small diameter is facing downward. Next, a plurality of langasite raw materials G are filled on the langasite seed crystal S. Next, the temperature is maintained for a specified time, the upper part of the Langasite seed crystal S and the Langasite raw material G are melted, and seeding for producing a Langasite type single crystal C is performed. The langasite seed crystal S is a nucleus for crystal growth, and in order to be integrated with the langasite raw material G, a part of the langasite seed crystal S is melted, but it must be prevented from being melted. After the seeding is completed, the crucible 1 for growing a Langasite type single crystal is gradually moved downward to pass the temperature gradient formed in the furnace. In this way, the raw material is cooled and solidified according to the crystal orientation of the Langasite seed crystal S to grow a single crystal, thereby producing a Langasite type single crystal C.

Seeding is performed by melting the upper part of the Langasite seed crystal S and the Langasite raw material G to form a stable solid-liquid interface, and the temperature of the solid-liquid interface and the holding at that temperature. Time is an important factor in seeding. This is because the crushed layer formed at the time of processing is present near the surface of the Langasite seed crystal S, and this crushed layer needs to be melted. This is also because it is necessary to form a solid-liquid interface before all the Langasite seed crystals S are melted. In order to satisfy the above requirements, the temperature T of the interface P between the Langasite seed crystal S and the Langasite raw material G is
Preferably 1496 to 1516 ° C., more preferably 1
The crucible 1 for growing a Langasite type single crystal is set at a position of 502-1510 ° C. The temperature at the interface between the langasite seed crystal S and the langasite raw material G is preferably measured by a thermocouple installed on the same plane as the interface and near the outside of the crucible 1 for growing a langasite type single crystal. Thereby, the temperature of the interface between the Langasite seed crystal S and the Langasite raw material G can be measured with high accuracy.

When the Langasite type single crystal growing crucible 1 is moved downward, the moving speed is 0.3 to
It is preferably 3 mm / hour. The moving speed for moving the Langasite type single crystal growing crucible 1 downward is 0.
When it is 3 to 3 mm / hour, the growing Langasite-type single crystal C can be passed through the optimum temperature gradient for crystal growth, so that a more uniform Langasite-type single crystal C can be produced. Further, it is preferable not to perform a rapid temperature decrease after the crystal growth. When the temperature is rapidly lowered, stress is generated in the single crystal, which may cause cracks.

According to the method for producing a Langasite type single crystal of the above-mentioned embodiment, a uniform Langasite type single crystal can be obtained without forming a secondary phase. The Langasite-type single crystal thus obtained is of high quality and therefore SA
It is suitable as a material for W devices. Further, since the secondary phase is not formed, the work of cylindrical grinding when the langasite seed crystal is repeatedly used is simplified, and as a result, the method for producing a langasite type single crystal becomes efficient.

[0019]

[Examples] [Example 1] Hereinafter, a method for producing a Langasite type single crystal of the present invention will be described in more detail with reference to Examples and Comparative Examples. First, the stoichiometric ratio of La ₂ O ₃ is 30 m
ol%, Ga ₂ O ₃ 50 mol%, SiO _{2 20} mo
Each oxide was weighed by a balance so as to be 1%. these,
After thoroughly mixing with a mixer,
It was calcined at 00 to 1300 ° C. for 5 hours. After pulverizing this powder, it was filled in a mold having an inner diameter of the platinum-made crucible 1 for growing a single crystal of Langasite or less and subjected to rubber pressing by hydrostatic pressure to obtain a Langasite raw material G having a cross-sectional diameter of 51.5 mm. It was

In order to grow a Langasite type single crystal C, a platinum single crystal growing crucible having a thickness of 0.15 mm, a straight body inner diameter of 52 mm, a bottom inner diameter of 44 mm, a taper angle of 7.6 ° and a height of 200 mm. First, the inner diameter of the upper surface is 51.5
mm, a taper angle of 8.1 °, and a height of 30 mm were filled with Langasite seed crystal S. Further, a plurality of langasite raw materials G were filled on it, and a lid 7 made of platinum foil for preventing dust from falling was placed on the opening of the langasite type single crystal growing crucible 1. Then, the Langasite-type single crystal growing crucible 1 filled with the Langasite seed crystal S and the Langasite raw material G was placed on the crucible receiver 5 made of porous alumina. Since the thickness of the langasite type single crystal growing crucible 1 was thin, a hard alumina tube 8 was covered around the langasite type single crystal growing crucible 1 for protection. A hole was made in one place of this alumina tube 8, the thermocouple 6 was inserted from there, and the contact point of the thermocouple 6 was brought into contact with the crucible 1 for growing a Langasite type single crystal. The contact point of the thermocouple was located on the same plane as the langasite seed crystal S and the langasite raw material G and in the vicinity of the crucible 1 for growing a langasite type single crystal.

This Langasite type single crystal growing crucible 1
Is set at the bottom of the furnace. The heater of the furnace was made of Super Kanthal that can be heated at a high temperature, and the upper, middle, and lower three-zone heaters could be controlled independently, and the length of each heater was 200 mm. The temperature of the upper heater is 15
The temperature was set to 50 ° C. and the temperature of the lower heater was set to 1450 ° C., and the temperature of the furnace was raised. After the temperature rise is completed and the temperature inside the furnace is stabilized, a crucible for growing a Langasite type single crystal 1
Was raised at a slow speed. Since a temperature gradient was formed in the furnace in the vertical direction, the temperature inside the crucible increased as it moved to the upper part of the furnace, and the Langasite raw material G was melted to form a Langasite melt.

While monitoring the temperature around the position of the Langasite-type single crystal growing crucible 1 formed by the melt with the thermocouple 6, the position of the Langasite-type single crystal growing crucible 1 is raised by several mm and the temperature is raised. Stabilized. The process of raising the temperature of the crucible 1 for growing a Langasite type single crystal and then stabilizing the temperature was repeated to obtain 1496 when the temperature was stable.
The crucible 1 for growing a Langasite type single crystal was raised so as to be in the range of ˜1516 ° C. Then, after holding for several hours, the Langasite-type single crystal growth crucible 1 was lowered at 0.5 mm / hour to start the growth. Descent distance 22
It was set to 0 mm, and the growth was completed in about 18 days. After the growth was completed, the crucible 1 for growing the Langasite type single crystal was peeled off, and the ingot of the Langasite type single crystal C was taken out. The length of the ingot was 170 mm.

[Comparative Example 1] A Langasite single crystal was prepared in the same manner as in Example 1 except that the taper angle of the Langasite seed crystal S was set to 7.6 °, which was the same as the taper angle of the crucible for growing a Langasite single crystal. Crystal C was produced.

[Comparative Example 2] A Langasite type single crystal C was prepared in the same manner as in Example 1 except that the Langasite type single crystal growing crucible 1 having no taper and the Langasite seed crystal S were used. .

In the method for producing the Langasite-type single crystal C of Example 1, the taper angle of the Langasite-type single crystal growing crucible 1 is 7.6 ° and the taper angle of the Langasite-type single crystal S is 8.1 °. Therefore, the peripheral portion of the maximum diameter of the Langasite seed crystal S is in contact with the inner wall of the tapered portion of the Langasite type single crystal growing crucible 1, and the Langasite type single crystal growing crucible 1 and the Langasite seed crystal. The melt did not enter between S and S. Therefore, a uniform langasite type single crystal C was obtained without forming a secondary phase. Moreover, the Langasite seed crystal S could be repeatedly used without cylindrical grinding. On the other hand, in the method for producing the Langasite-type single crystal C of Comparative Example 1, since the taper angle of the Langasite-type single crystal S and the taper angle of the Langasite-type single-crystal growing crucible 1 were the same, The portion of the circumference of the maximum diameter of S was in contact with the inner wall of the taper portion of the crucible 1 for growing a Langasite type single crystal, but a very small amount of melt penetrated from a slight gap.
Since the infiltration amount of the melt was extremely small, no secondary phase was formed and a uniform langasite type single crystal C was obtained. However, since a small polycrystal was formed, the Langasite seed crystal S could not be used repeatedly unless it was cylindrically ground. Further, in the method for producing the langasite type single crystal C of Comparative Example 2, since the langasite type single crystal growing crucible 1 and the langasite seed crystal S were not tapered, the langasite type single crystal growing crucible. The melt penetrated into the gap between 1 and the Langasite seed crystal S, and a secondary phase was formed. Therefore, the obtained langasite-type single crystal C was non-uniform, and the langasite seed crystal S could not be repeatedly used without cylindrical grinding.

[0026]

According to the method for producing a Langasite type single crystal according to the present invention, since the peripheral portion of the maximum diameter of the seed crystal is in contact with the inner wall of the tapered portion of the crucible for growing the single crystal, the seed crystal and the Langasite type crystal are formed. Since the melt does not penetrate into the crucible for growing a single crystal and a polycrystalline phase is not formed, a uniform Langasite type single crystal can be produced. Further, since the polycrystalline phase is not formed, it is possible to simplify the work such as cylindrical polishing performed when the seed crystal is repeatedly used, and as a result, the Langasite type single crystal is efficiently produced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a furnace used in an embodiment of a method for producing a Langasite type single crystal according to the present invention.

FIG. 2 is a cross-sectional view showing a crucible for growing a Langasite type single crystal and a Langasite seed crystal used in one embodiment of a method for producing a Langasite type single crystal according to the present invention.

FIG. 3 is a graph showing a temperature gradient of a furnace used in an embodiment of a method for producing a Langasite type single crystal according to the present invention.

FIG. 4 is a cross-sectional view showing an example of a furnace for performing a conventional method for producing a Langasite type single crystal.

[Explanation of symbols]

1. Langasite single crystal growth crucible G. Langasite raw material (raw material) S. Langasite seed crystal (seed crystal) C. Langasite type single crystal (single crystal)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Satoshi Uda             Saitama Prefecture Chichibu-gun Yokose-cho 2270 Yokoze             Ryo Materials Co., Ltd. Ceramics Factory Den             Child Device Development Center (72) Inventor Keigo Hoshikawa             6 Shin-Nagano Education in Nishi-Nagano, Nagano City, Nagano Prefecture             Undergraduate F term (reference) 4G077 AA02 BD15 CD02 ED01 EG01                       MA01 MB04

Claims (3)

[Claims] 1. A seed crystal is filled in a lower part of a crucible for growing a Langasite type single crystal, and a raw material is filled on the seed crystal so that the seed crystal and the raw material have a temperature gradient in a vertical direction. After melting in a vertical furnace, a method of producing a Langasite-type single crystal in which the Langasite-type single crystal growing crucible is vertically moved to produce a Langasite-type single crystal, wherein the Langasite-type single crystal is produced. The crystal-growing crucible and the seed crystal have a tapered shape with a smaller diameter toward the bottom, and the taper angle of the seed crystal is larger than the taper angle of the Langasite-type single-crystal growing crucible. Method for producing langasite type single crystal. 2. The seed crystal has a taper angle of 0.5 than a taper angle of the crucible for growing a Langasite type single crystal.
The method for producing a Langasite type single crystal according to claim 1, wherein the Langasite type single crystal is larger by 1 °. 3. The Langasite-type single crystal according to claim 1, wherein the moving speed for vertically moving the Langasite-type single crystal crucible is 0.3 to 3 mm / hour. Manufacturing method.