JP4168796B2 - Single crystal pulling apparatus crucible and single crystal pulling apparatus - Google Patents

Description

【００２４】
次に、円筒状部材と円板状部材との板厚比を変化させて構成した坩堝にてランガサイト単結晶を育成した。板厚比は、側壁に対する底部厚み比として、９０％、８０％、５０％、２０％とし、それぞれ実施例１から実施例４とした。また、比較例として厚み比が１００％の従来の坩堝にてランガサイト単結晶を育成した。
各実施例における結晶に対し、上部（直胴下３０ｍｍ位置）、中部（直胴下９０ｍｍ位置）、下部（直胴下１５０ｍｍ位置）のそれぞれをスライスした。そして、得られたランガサイト単結晶の均質性を表面弾性波速度のバラツキとして評価するために、さらにラッピング、ポリッシングにより、図５に示す圧電デバイス用基板３０を作製した。この圧電デバイス用基板３０の表面に、一対のアルミ製励振電極３１ａ、３１ｂと、シリコン系樹脂製の一対の吸音部３２ａ、３２ｂとを形成してＳＡＷフィルタ３３を作製した。
なお、比較例の場合、直胴下部に二次相が発生したので結晶上部と中部のみを使用した。
【００２５】
そして、ネットワークアナライザを用いてＳＡＷフィルタ３３の入力端子に交流信号をかけ、出力端子からの出力信号を測定し、周波数走査によって出力信号と入力信号との相対振幅の周波数特性を得て、このピーク値から挿入損失が−１０ｄＢとなる通過帯域中心点の周波数である中心周波数ｆｃを測定した。
ここで、表面弾性波速度は、ｖ＝ｆｃ・２ｄという関係式によって求める。式中の２ｄは、ＳＡＷフィルタ３３の励振電極３１ａ、３１ｂの配線周期であり電子顕微鏡で測定して求めた。測定結果を表２に示す。
【００２６】
【表２】

【００２７】
各実施例における表面弾性波速度の平均値は２７４０．７３ｍ／ｓ、バラツキの平均値は９２．２７ｐｐｍとなった。このことから、均質性の優れた圧電デバイス用基板の目安とされる１００ｐｐｍ以下を実現できたこととなり、結晶の均質性を向上させることができた。
一方、比較例では、それぞれ、２７４０．２３ｍ／ｓ、２５０．６３ｐｐｍとなり、特に結晶の育成方向の表面弾性波のバラツキは４００ｐｐｍ以上であり、表面弾性波素子としては大きすぎる結果となった。
【００２８】
【発明の効果】
以上説明した本発明においては以下の効果を奏する。
本発明の単結晶引上用坩堝によれば、適切な温度勾配を容易に設けることができ、坩堝内に発生する自然対流が強くなることで、単結晶育成時における固液界面の成長速度を一様にするので、二次相等の異相及び結晶欠陥が発生するのを抑制し、単結晶構造の均一化及び長尺化を図ることができる。
【００２９】
また、本発明の単結晶引上装置によれば、二次相等の異相及び結晶欠陥の発生を抑制し、均一化及び長尺化された単結晶を得ることができる。また、得られた単結晶から切り出された圧電デバイス用基板は、その表面弾性波速度のバラツキを大幅に減少させ、この基板上に作製する表面弾性波デバイス等の表面弾性波素子の製造歩留まりを大幅に向上することができる。
【図面の簡単な説明】
【図１】 本発明の一実施形態における単結晶引上装置の要部断面図である。
【図２】 本発明の一実施形態における単結晶引上装置用坩堝を示す断面図である。
【図３】 本発明の一実施形態における単結晶引上装置用坩堝の他の例を示す断面図である。
【図４】 本発明に係る実施例において、溶融した単結晶原料の融液中及び融液上の温度を示すグラフである。
【図５】 本発明に係る実施例において、育成したランガサイト単結晶で作製したＳＡＷフィルタを示す斜視図である。
【符号の説明】
１０ 単結晶引上装置
１１ 加熱コイル
１２、２６、２８、２９ 坩堝（単結晶引上装置用坩堝）
１６、２７ 円筒状部材
１７、２５ 円板状部材
１８ Ｌａ₃Ｇａ₅ＳｉＯ₁₄（ランガサイト）単結晶
１９ 原料
２０ 融液
２５ａ 中央部
２５ｂ 周辺部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a crucible for a single crystal pulling apparatus and a single crystal pulling apparatus for pulling and growing a single crystal of La ₃ Ga ₅ SiO ₁₄ (Langasite ) .
[0002]
[Prior art]
A single crystal of La ₃ Ga ₅ SiO ₁₄ (Langasite) has a low rate of change in elastic wave propagation speed and frequency due to temperature and a large electromechanical coupling coefficient indicating the magnitude of piezoelectricity. Research has been conducted on substrate materials for piezoelectric devices. That is, this langasite single crystal has a temperature characteristic equivalent to that of quartz and has an electromechanical coupling coefficient as large as three times that of quartz. Therefore, when a langasite single crystal is used, it is often used for mobile phones and the like. Therefore, it is possible to reduce the bandwidth and size of the existing SAW filter (see, for example, Patent Document 1).
As a method for producing this single crystal, there is a single crystal growing method by the Czochralski method which can set the growing speed fast.
[0003]
In the growing method by this Czochralski method, after filling a single crystal raw material in a crucible serving as a container in advance, this is heated and melted, a seed crystal called a seed is brought into contact with the melt, and then rotated. Pull it up slowly and leave the melt to some extent to finish the growth.
An apparatus using induction heating is known as one of the single crystal pulling apparatuses used at this time. In this apparatus, a crucible composed of a bottom and a side wall is arranged in a heating coil having a vertical central axis. The crucible is induction-heated by the heating coil to melt the raw material inside, and a single crystal is obtained from the stored melt. A single crystal is grown by pulling up.
[0004]
However, even if the crucible was induction-heated by the heating coil, the bottom part was farther from the heating coil than the side wall part, so that eddy current was not generated and heat generation was insufficient. Therefore, the natural convection generated in the crucible becomes weak and the growth rate of the melt interface is not stable, so the variation in surface acoustic wave velocity in the wafer surface made from the obtained langasite single crystal is large and uniform. It was difficult to grow a single crystal.
[0005]
In addition, since it is difficult to obtain an appropriate temperature gradient in which the temperature at the lower part of the crucible is higher than that at the upper part of the crucible, it is difficult to release latent heat when the crystal is grown from the melt during crystal growth. May occur, which may affect the lengthening of the crystal.
Conventionally, as a crucible for a single crystal pulling apparatus that solves these problems, in order to obtain an appropriate temperature gradient, an auxiliary heater is provided at the bottom of the crucible and heated, so that the temperature at the bottom of the crucible becomes higher than that at the top. A correction is proposed in this way (see, for example, Patent Document 2).
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-126209 [Patent Document 2]
Japanese Patent Laid-Open No. 63-103889
[Problems to be solved by the invention]
However, in the conventional crucible for a single crystal pulling apparatus, a space for arranging the auxiliary heater is required, and it is necessary to control the auxiliary heater separately from the heating coil. It was difficult to control by applying a gradient. Therefore, it was still difficult to obtain a long single crystal with a single phase.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a crucible for a single crystal pulling apparatus and a single crystal pulling apparatus that can easily provide an appropriate temperature gradient.
[0008]
[Means for Solving the Problems]
The present invention employs the following means in order to solve the above problems.
The crucible for a single crystal pulling apparatus according to the present invention is arranged in a heating coil having a vertical central axis, and La ₃ Ga ₅ SiO ₁₄ from a melt that is heated by induction heating by the coil to melt and store the raw materials inside. A crucible for a single crystal pulling apparatus for pulling up a single crystal of (Langasite), comprising a cylindrical member constituting a side wall and a disk-like member constituting a bottom, and the cylindrical member and the circle Each of the plate-like members is made of iridium, and the thickness of the disk-like member is 80% or less of the plate thickness of the cylindrical member .
[0009]
In this crucible for single crystal pulling apparatus , La ₃ Ga ₅ SiO ₁₄ (Langasite) single crystal raw material is stored, so that a single growth rate of the Langasite single crystal at the interface of the melt is obtained when growing the single crystal. Can be nurtured. In addition, since crystal defects are suppressed, a long langasite single crystal can be produced. Further, since iridium is used as the metal constituting the crucible, efficient high-frequency induction heating can be performed, and a single crystal raw material having a high temperature melting point can be melted.
Further, since the thickness of the disk-shaped member is 80% or less of the thickness of the cylindrical member, the difference in thickness between the disk-shaped member and the cylindrical member becomes clear from the experimental data described later, and the surface elasticity It is possible to obtain a langasite single crystal in which the variation in wave velocity is small and the length of the straight body is long and the generation of crystal defects is suppressed.
[0014]
In the single crystal pulling apparatus of the present invention, a metal crucible is arranged in a heating coil having a vertical center axis, and the crucible is induction-heated by the coil to melt the raw material inside and store the single material from the stored melt. A single crystal pulling apparatus for pulling a crystal, wherein the crucible is a crucible for a single crystal pulling apparatus according to the present invention.
This single crystal pulling apparatus can induce a strong natural convection in the crucible by causing a large amount of eddy current to flow through the lower surface of the crucible to induce induction heating. At the same time, it is possible to maintain an appropriate temperature gradient in which the lower side of the crucible is hotter than the upper side. Moreover, a crystal defect is suppressed and a long single crystal can be manufactured.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the present invention will be described with reference to FIGS.
A single crystal pulling apparatus 10 shown in FIG. 1 includes a heating coil 11, a single crystal pulling apparatus crucible 12, a heat insulating material 13, a heat reflector 14, and a pulling shaft 15.
The heating coil 11 has a vertical central axis and is connected to an external high-frequency power source (not shown).
The crucible 12 is arranged in the heating coil 11 with the same central axis, and includes a cylindrical member 16 constituting a side wall and a disk-like member 17 constituting a bottom part, as shown in FIG. ing.
The cylindrical member 16 and the disc-like member 17 are made of iridium, and the thickness of the disc-like member 17 is thinner than that of the cylindrical member 16 (for example, 80% of the thickness of the cylindrical member 16). ing.
In the crucible 12, a raw material 19 of the langasite single crystal 18 is disposed. After being heated by induction heating by the heating coil 11, the raw material 19 is melted and becomes a melt 20. Is stored inside.
[0016]
The heat insulating material 13 insulates between the heating coil 11 and the crucible 12, and is disposed inside the external heat insulating material 21 made of alumina in a cylindrical shape and inside the external heat insulating material 21, and formed in a cylindrical shape. And an internal heat insulating material 22 made of zirconia for accommodating the crucible 12 therein.
The heat reflector 14 reflects the heat radiated from the periphery of the langasite single crystal 18 in order to prevent the pulled langasite single crystal 18 from rapidly cooling, and is made of the same material as the crucible 12. Or it is comprised by the cylindrical shape with platinum. The heat reflector 14 is disposed above the internal heat insulating material 22 via an alumina intermediate heat insulating material 23 formed in a cylindrical shape.
The pulling shaft 15 has a Langasite seed crystal 24 fixed to the tip, and is inserted into the crucible 12 from above the crucible 12. By adding a predetermined rotational speed and a pulling speed to the pulling shaft 15, the melt 20 is pulled up above the crucible 12 to grow the langasite single crystal 18.
[0017]
Next, a method for producing the langasite single crystal 18 using the single crystal pulling crucible 12 and the single crystal pulling apparatus 10 according to the present invention will be described.
First, lanthanum oxide La ₂ O ₃ (30 mol%), gallium oxide (III) Ga ₂ O ₃ (50 mol%), and silicon dioxide SiO ₂ (20 mol%) are weighed in a stoichiometric ratio. These are mixed sufficiently to obtain a mixed powder, which is pressed and molded so as to have a size of 100 mm × 60 mm, and then put into a rubber bag and vacuumed to be brought into close contact with the rubber. Further, an isostatic rubber press is performed to remove the rubber and then sinter to obtain a pellet-shaped raw material 19.
This raw material 19 is inserted into the crucible 12 as shown in FIG.
[0018]
Subsequently, the raw material 19 is melted.
A high-frequency voltage is applied to the heating coil 11 from a high-frequency power source (not shown) to pass a current. Then, a magnetic field is generated in the heating coil 11 and the crucible 12, and an eddy current associated therewith is generated on the surfaces of the cylindrical member 16 and the disk-shaped member 17. The crucible 12 is induction-heated by this eddy current and the electric resistance of iridium constituting the crucible 12, and the raw material 19 inside is heated and melted.
At this time, the cylindrical member 16 located closer to the heating coil 11 is more likely to generate eddy currents than the disk-shaped member 17. However, since the thickness of the disk-shaped member 17 is thinner than the thickness of the cylindrical member 16, the entire disk-shaped member 17 is likely to generate heat, and the temperature becomes higher with higher efficiency and faster than the cylindrical member 16. Thus, an appropriate temperature gradient can be applied to the crucible 12 so that the lower portion has a higher temperature than the upper portion, and the raw material 19 is melted to obtain a melt 20 having strong internal convection.
[0019]
Next, the langasite single crystal 18 is grown from the melt 20 at a predetermined temperature.
The pulling shaft 15 is inserted into the crucible 12 and the langasite seed crystal 24 is immersed in the melt 20 to add a predetermined rotation speed and pulling speed. Then, the langasite single crystal 18 is precipitated based on the langasite seed crystal 24.
At this time, since an appropriate temperature gradient is applied to the melt 20, the growth rate at the interface is constant, and a uniform langasite single crystal 18 is obtained.
[0020]
According to the single crystal pulling crucible 12 and the single crystal pulling apparatus 10, the disk-shaped member 17 is set thinner than the cylindrical member 16 and the bottom is efficiently induction-heated. Thus, a single temperature gradient can be easily added, and the langasite single crystal 18 having a uniform growth rate at the interface of the melt 20 can be grown. Further, since crystal defects are suppressed, a long langasite single crystal 18 can be manufactured. Further, the piezoelectric device substrate cut out from the obtained langasite single crystal 18 greatly reduces the variation in the surface acoustic wave velocity, and the surface acoustic wave device such as the surface acoustic wave device manufactured on the substrate is reduced. The manufacturing yield can be greatly improved.
[0021]
The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, in the above embodiment, the disc-like member 17 of the crucible 12 has a uniform thickness, but as shown in FIG. 3A, the central portion 25a of the disc-like member 25 is a disc-like member. The same operation and effect can be obtained with the crucible 26 having a plate thickness thinner than the peripheral portion 25b of 25.
Further, as shown in FIGS. 3B and 3C, a crucible 28 in which a tapered portion 27a is formed so that the upper portion of the cylindrical member 27 is thick and the lower portion is thin, and a step portion 27b are formed. even side walls of which crucible 29 is formed, it is possible to obtain the same effects.
[0022]
【Example】
As this example, a langasite single crystal having a diameter of 115 mm and a straight body length of 180 mm was grown from the above-described single crystal pulling crucible 12 and single crystal pulling apparatus 10 according to the embodiment. Further, as a comparative example, a Langasite single crystal having the same shape was grown using a conventional crucible.
At this time, the temperature gradient was evaluated by measuring the temperature in the melt and on the melt with a thermocouple. The results are shown in Table 1 and FIG.
As a result, the Langasite single crystal of this example has a larger temperature gradient than the conventional case both in the melt and on the melt, and there is no occurrence of crystal defects such as secondary phases. there were.
[0023]
[Table 1]

[0024]
Next, a langasite single crystal was grown in a crucible configured by changing the thickness ratio of the cylindrical member and the disk-shaped member. The plate thickness ratios were 90%, 80%, 50%, and 20% as the bottom thickness ratio with respect to the sidewalls, respectively, and Example 1 to Example 4, respectively. As a comparative example, a langasite single crystal was grown in a conventional crucible having a thickness ratio of 100%.
With respect to the crystal in each example, each of the upper part (position 30 mm below the straight cylinder), the middle part (position 90 mm below the straight cylinder), and the lower part (position 150 mm below the straight cylinder) was sliced. Then, in order to evaluate the homogeneity of the obtained langasite single crystal as variations in surface acoustic wave velocity, a piezoelectric device substrate 30 shown in FIG. 5 was produced by lapping and polishing. A pair of aluminum excitation electrodes 31a and 31b and a pair of sound absorbing portions 32a and 32b made of silicon resin were formed on the surface of the piezoelectric device substrate 30 to produce a SAW filter 33.
In the case of the comparative example, since the secondary phase was generated at the lower part of the straight cylinder, only the upper part and the middle part of the crystal were used.
[0025]
Then, an AC signal is applied to the input terminal of the SAW filter 33 using a network analyzer, the output signal from the output terminal is measured, and the frequency characteristic of the relative amplitude between the output signal and the input signal is obtained by frequency scanning. The center frequency fc, which is the frequency at the center point of the passband where the insertion loss is −10 dB, was measured from the value.
Here, the surface acoustic wave velocity is obtained by a relational expression of v = fc · 2d. 2d in the equation is the wiring period of the excitation electrodes 31a and 31b of the SAW filter 33, and was obtained by measurement with an electron microscope. The measurement results are shown in Table 2.
[0026]
[Table 2]

[0027]
In each Example, the average value of the surface acoustic wave velocity was 2740.73 m / s, and the average value of the variation was 92.27 ppm. From this, it was possible to achieve 100 ppm or less, which is a standard for a piezoelectric device substrate having excellent homogeneity, and the crystal homogeneity could be improved.
On the other hand, in the comparative example, it was 2740.23 m / s and 250.63 ppm, respectively, and especially the variation of the surface acoustic wave in the crystal growth direction was 400 ppm or more, which was too large as a surface acoustic wave device.
[0028]
【The invention's effect】
The present invention described above has the following effects.
According to the single crystal pulling crucible of the present invention, an appropriate temperature gradient can be easily provided, and the natural convection generated in the crucible becomes strong, so that the growth rate of the solid-liquid interface during single crystal growth can be increased. Since they are uniform, it is possible to suppress the occurrence of heterogeneous phases such as secondary phases and crystal defects, and to make the single crystal structure uniform and long.
[0029]
Moreover, according to the single crystal pulling apparatus of the present invention, generation of a heterogeneous phase such as a secondary phase and crystal defects can be suppressed, and a uniform and elongated single crystal can be obtained. In addition, the piezoelectric device substrate cut out from the obtained single crystal greatly reduces the variation in the surface acoustic wave velocity, and the production yield of surface acoustic wave devices such as surface acoustic wave devices fabricated on this substrate is reduced. It can be greatly improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a main part of a single crystal pulling apparatus according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a crucible for a single crystal pulling apparatus according to an embodiment of the present invention.
FIG. 3 is a cross-sectional view showing another example of a crucible for a single crystal pulling apparatus according to an embodiment of the present invention.
FIG. 4 is a graph showing temperatures in and on the melt of a molten single crystal raw material in an example according to the present invention.
FIG. 5 is a perspective view showing a SAW filter made of a grown langasite single crystal in an example according to the present invention.
[Explanation of symbols]
10 Single Crystal Pulling Device 11 Heating Coils 12, 26, 28, 29 Crucible (Crucible for Single Crystal Pulling Device)
16, 27 Cylindrical members 17, 25 Disc-shaped members 18 La ₃ Ga ₅ SiO ₁₄ (Langasite) single crystal 19 Raw material 20 Melt 25a Central part 25b Peripheral part

Claims (2)

Single crystal pulling which is arranged in a heating coil having a vertical central axis and which pulls up a single crystal of La ₃ Ga ₅ SiO ₁₄ (Langasite) from the melt melted by induction heating by the coil to melt the raw material inside. A crucible for the upper device,
It is composed of a cylindrical member that constitutes the side wall and a disc-like member that constitutes the bottom, and the cylindrical member and the disc-like member are each formed of iridium,
A crucible for a single crystal pulling apparatus , wherein the thickness of the disk-shaped member is 80% or less of the thickness of the cylindrical member . This is a single crystal pulling apparatus in which a metal crucible is arranged in a heating coil having a vertical central axis, and the crucible is induction-heated by the coil to melt the raw materials inside and pull up the single crystal from the stored melt. And
The single crystal pulling apparatus according to claim 1, wherein the crucible is a crucible for a single crystal pulling apparatus according to claim 1 .

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