JP2002255691A - Pulling method of langisite monocrystal and langisite monocrystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which is high in manufacturing efficiency of wafer and obtains high crystalline langisite monocrystal. SOLUTION: Face (01-11) of seed crystal is brought into contact with fused liquid which is prepared by melting raw material, the seed crystal is pulled in the perpendicular direction to the crystalline face while rotating the seed crystal and, thereby, the langisite monocrystal C is manufactured. Therein, the rotation of the seed crystal is gradually decreased in the range of 20-2 rpm and, at the same time, the seed crystal is pulled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a surface acoustic wave (Surfac).
The present invention relates to a method for pulling a langasite single crystal and a langasite single crystal obtained by the pulling method, which are used for a substrate for a piezoelectric device or the like suitable for an e Acoustic Wave (SAW) filter or the like.

[0002]

2. Description of the Related Art FIG. 1 shows an example of a method of pulling (growing) a Langasite single crystal, which is one of oxide single crystals. In this example, the Czochralski method (CZ method) is used. Incidentally, langasite single crystal is generally represented by the chemical formula La ₃ Ga ₅ SiO _14. The crystal is grown by using an iridium crucible 1 in a high-frequency heating and growing furnace.
An alumina-based or zirconia-based heat insulating material 2 is provided on the outside and the upper side to form a hot zone. A high-frequency work coil 3 for heating is provided outside the heat insulating material 2. In addition,
A thermocouple 4 is provided at the bottom of the crucible 1. At the time of growth, the metal oxides (La ₂ O ₃ , Ga ₂ O ₃ , Si
After mixing O ₂ ) at a predetermined mixing ratio, the mixture is charged into the crucible 1, heated and melted to obtain a melt L at a predetermined temperature.
Next, the seed crystal S is fixed to the pulling shaft 5 and the single crystal S is pulled up from the melt L at a predetermined rotation speed and a predetermined pulling speed, thereby growing the langasite single crystal C as shown in FIG. The automatic diameter control is performed based on a weight change signal detected by a weight sensor 6 connected to the lifting shaft 5.

In the conventional method of pulling a langasite single crystal, the pulling direction is perpendicular to the (0001) plane of the hexagonal crystal structure shown in FIG. 3 (Z-axis direction). In cutting out a wafer from a langasite single crystal, the cutting angle parallel to the Y50 plane is the most excellent cutting angle. Hereinafter, a wafer cut at this angle is referred to as a Y50 wafer. The Y50 surface is
As shown in FIG. 4, the Z axis is perpendicular to the (0001) plane, and the + X axis is

(Equation 2) Perpendicular to the Y axis

(Equation 3) , A plane perpendicular to an axis obtained by rotating the Y-axis by 50 degrees toward the Z-axis about the origin on the YZ plane. FIG. 5 is a schematic view showing a cut-out portion of a Y50 wafer in a langasite single crystal C manufactured by pulling up in the Z-axis direction. The cut-out portion is a hatched portion.

However, in the case of a langasite single crystal pulled in the Z-axis direction, there is a problem that dislocation defects are present in the Y50 wafer and the dislocation density is large. In addition, when cut out in parallel to the Y50 plane, there is a problem that the cut-out portion has a small volume as shown in FIG.

[0005] International Publication WO98 / 40544 discloses a method for pulling a langasite single crystal as described below which solves this problem. That is, in the langasite single crystal, the indexing by the hexagonal crystal structure is performed.

(Equation 4) (Hereinafter, referred to as (01 (-1) 1) plane) is shown in FIG.
(A), as shown in FIG. 6 (b), on the YZ plane, the Y axis is directed toward the Z axis with the origin at the center, and is 54.2.
A plane perpendicular to the axis rotated twice (hereinafter referred to as Y54 plane)
It is. And, in the langasite single crystal, Y50
The plane closest to the plane is the Y54 plane. FIG. 6A is an explanatory diagram showing a state viewed from the Z-axis direction when the langasite single crystal is defined by coordinates in a hexagonal system.
(B) is an explanatory view showing a state viewed from the + X axis direction.

Therefore, as shown in FIG. 7, the base of the cuboidal seed crystal is (01 (−)
1) The seed crystal is cut out so as to be a 1) face and one of the side faces is a face perpendicular to the + X axis (hereinafter referred to as a + X face), and this seed crystal is cut in the high-frequency heating and growing furnace shown in FIG. Then, the (01 (-1) 1) plane and the melt L are attached to the lifting shaft 5 so as to be parallel to each other, and as shown in FIG. As a result, a langasite single crystal C is obtained. In this langasite single crystal C, the (01 (-1) 1) plane and the Y50
Since the angle difference θ with the plane is small, for example, a portion shown by hatching in the figure can be cut out as a Y50 wafer,
It is possible to cut out a Y50 wafer without much waste compared to the related art. As a result, the wafer production efficiency is dramatically improved, and the yield is improved.

[0007]

However, this Y
In the pulling method using the 54 plane, the crystallinity of the langasite single crystal is low, and further improvement has been desired. Specifically, it has been desired to grow a crystal having a cylindrical shape with good symmetry and having no defects such as a secondary phase.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method of pulling a langasite single crystal having high crystallinity in a method of pulling a langasite single crystal using the Y54 plane. . Specifically, it is an object of the present invention to provide a method capable of growing a crystal having a cylindrical shape with good symmetry and having no defects such as a secondary phase.

[0009]

In order to solve the above-mentioned problems, a method for pulling a langasite single crystal according to the present invention provides a method in which a (01 (-1) 1) plane of a seed crystal is added to a melt obtained by melting a raw material. A method of producing a langasite single crystal by contacting and rotating the seed crystal in a direction perpendicular to the crystal plane while rotating the seed crystal, wherein the seed crystal is pulled while gradually reducing the rotation of the seed crystal within a range of 20 to 2 rpm. It is characterized by.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example of a method for pulling a langasite single crystal of the present invention will be described with reference to FIGS. For example, from a langasite single crystal manufactured by pulling up in the Z-axis direction by a conventional method, a substantially rectangular parallelepiped langasite seed crystal is formed as shown in FIG. 7 with at least one surface having a (01 (−1) 1) plane. Cut out so that. At this time, preferably, the bottom surface of the rectangular parallelepiped is (01 (−
1) The surface should be 1), and one surface of the side surface should be the + X surface. Then, for example, using the high frequency heating and growing furnace shown in FIG.
(-1) 1) The seed crystal S is fixed to the pulling shaft 5 so that the plane is parallel to the plane, and is perpendicular to the (01 (-1) 1) plane at a predetermined speed and rotation speed as shown in FIG. Then, a langasite single crystal C having an outer shape similar to that of the langasite single crystal shown in FIG. 2 is obtained.

At this time, the rotation speed of the seed crystal is set to 20 to 2 rpm.
Raise while gradually decreasing in the range of m. By gradually reducing the number of revolutions in this way, in the initial stage of crystal growth, the number of revolutions is large, so that a cylindrical crystal with good symmetry is grown, the growth proceeds, and at the stage where the crystal shape is stabilized, Since the number of rotations is small, a crystal without defects such as a secondary phase is grown. When the rotation speed is 20 rpm or more, vibrations are generated on the pulling shaft with an increase in the crystal diameter, and this vibration may increase the generation rate of the secondary phase rapidly. On the other hand, if it is 2 rpm or less, the shape may not be a cylindrical shape having good symmetry when growing the shoulder portion of the crystal.

The lifting speed is not particularly limited, but is, for example, 0.5 to 5 mm / h. The oxygen partial pressure of the gas in the high-frequency heating and growing furnace is preferably 1 to 8% from the viewpoint of suppressing evaporation of the raw material and damage to the crucible 1 made of iridium. The pulling method is not particularly limited, and a known method such as the Czochralski method shown in FIG. 1 or another ordinary single crystal growing method, for example, the Bridgman method can be applied.

The langasite single crystal thus pulled out is cut off, and preferably cooled at a cooling rate of 10 to 70 ° C./h according to a temperature pattern controlled by a computer program, as shown in FIG. Y50
Cut out the wafer.

As described above, the langasite single crystal is generally represented by the chemical formula La ₃ Ga ₅ SiO ₁₄ . The langasite single crystal of the present invention only needs to be one in which only a langasite phase is observed by X-ray diffraction. That is, the present invention is not limited to the one represented by this chemical formula, and a part of the metal element may be replaced by another element, or the number of oxygen may be out of the above stoichiometric composition. Further, inevitable impurities may be contained. Therefore, the composition of the seed crystal and the raw material used as the melt L is appropriately selected depending on the desired composition of the langasite single crystal.

As described above, in the method of pulling a langasite single crystal of the present invention, a Y50 wafer having high crystallinity can be obtained, and a large amount of Y50 can be obtained from the langasite single crystal.
Wafers can be cut out. Further, the langasite single crystal obtained by the pulling method of the present invention has fewer dislocation defects and a lower dislocation density than the langasite single crystal obtained by pulling in the direction parallel to the Z axis. .

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. (Example) From the langasite single crystal pulled in the Z-axis direction, as shown in FIG. 7, the bottom surface was (01 (-1) 1).
A rectangular parallelepiped block in which one of the face and the side face is the + X face was cut out to obtain a seed crystal S. The growth of langasite single crystals
Czochralski method was performed using the high frequency heating and growing furnace shown in FIG. In this high-frequency heating and growing furnace, the weight sensor 6 is a load cell, and the lifting shaft 5 has a metal shaft below the weight sensor 6 and a holding rod made of a high-purity alumina tube below the metal shaft via a metal chuck. A rod having a structure in which a seed crystal S was fixed to the tip of a rod with an iridium bin was used. High-purity alumina and iridium bottles are used in consideration of heat resistance.

First, the seed crystal S is replaced with its (01 (-
1) It was attached to the lifting shaft 5 so that the 1) plane was parallel to the liquid surface of the melt L. And, diameter 120mm x depth 12
La ₂ O ₃ was placed on an iridium crucible 1 having a thickness of 0 × 2 mm.
There 47.4 to 49.1 wt%, Ga ₂ O ₃ is from 45.0 to 46.
A total of about 7 kg of a metal oxide raw material mixed so as to be 9% by weight and SiO _{2 in a range} of 5.2 to 6.5% by weight so as to be 100 g less than the maximum charging amount of the crucible 1 is charged.
Heated and melted. Then, in order to sufficiently decompose the langasite cluster in the melt L, about 120
After holding for about 0 minutes (20 hours), the seed crystal S was pulled up while rotating. During the heating and melting of the raw material and the pulling of the single crystal C, a heat insulating material 2 is disposed for the purpose of keeping the hot zone warm and protecting the high-frequency work coil 3, and an after-product made of iridium is placed on the crucible 1. Heater (diameter 120mm, height 100mm, thickness 2mm)
Was placed. Rotation speed of seed crystal S during pulling is 20 rpm
From 2 to 2 rpm, and the pulling speed is 0.5 to
5 mm / h. Further, for the growth of the langasite single crystal C, a neck portion was formed, a shoulder was grown, and a straight body was grown after the seed touch according to the conventional method. The straight body has a diameter of 90
mm and a length of 90 mm.

Next, the obtained langasite single crystal was cut off and cooled. This langasite single crystal and the melt L
Cooling takes about 50 hours at 1500 ° C to 25 ° C (room temperature)
Cooled down according to a temperature pattern controlled by a computer program. The cooling rate was 30 ° C./h. Next, a plate of Y50 face was cut out from the langasite single crystal using a wire saw, lapped and polished, and one face was mirror-finished to obtain a Y50 wafer.

Comparative Example 1 Rotation at the time of lifting was 2 rpm
A langasite single crystal was produced in the same manner as in the example, except that it was kept constant.

Comparative Example 2 Rotation at the time of lifting was 20 rpm
A langasite single crystal was produced in the same manner as in the example except that m was constant.

Comparative Example 3 A langasite single crystal was produced in the same manner as in the example except that the pulling direction was changed to the Z-axis direction, and a Y50 wafer was cut out.

First, the crystallinity of the langasite single crystals obtained in Examples, Comparative Examples 1 and 2 having different rotation speeds at the time of pulling was evaluated as follows. That is, a cylindrical shape having a good symmetry can be obtained by using a 3-inch wafer (diameter of 76.2 mm).
Can be determined on the basis of whether or not the wafer can be acquired. The presence or absence of the secondary phase was visually determined. Note that it is practically impossible to obtain a wafer from a crystal in which a secondary phase has occurred. As a result, a 3 inch wafer could be obtained from the langasite single crystal of the example, and no secondary phase was generated. In the case of the langasite single crystal of Comparative Example 1, a 3-inch wafer could not be obtained, and no secondary phase was generated. In the case of the langasite single crystal of Comparative Example 2, a 3-inch wafer could be obtained in terms of size, but a secondary phase was generated and a 3-inch wafer could not be obtained. Therefore, in Examples having different rotation speeds, Comparative Example 1, and Comparative Example 2, it was confirmed that only the langasite single crystal of the example according to the present invention can obtain a 3-inch Y50 wafer, The effect of the present invention has been clarified.

Further, the Y50 wafers obtained in Example and Comparative Example 3 were immersed in a solution having a weight ratio of HCl: H ₂ O of 1: 1 at 70 ° C. for 4 minutes, whereby dislocation on the wafer surface. And the dislocation density was measured. As a result, the measurement result of the Y50 wafer of the example was 1-3 × 10 ⁴ cm ⁻² , and almost no dislocation appeared. On the other hand, the measurement result of the Y50 wafer of Comparative Example 3 was 2.7 × 10 ⁶ cm ⁻² . In the example and the comparative example 3, the number of Y50 wafers that can be cut out from the same size langasite single crystal C was about 25 in the comparative example 3 and about 90 in the example.
Therefore, in the examples according to the present invention, it was also confirmed that the dislocation density of the Y50 wafer was low and the production efficiency was high.

When a 4-inch wafer was evaluated in the same manner, the same results as in a 3-inch wafer were obtained.

[0025]

As described above, according to the method for pulling a langasite single crystal of the present invention, a Y50 wafer having a low dislocation density and a high crystallinity can be obtained, and a large amount of Y50 wafers can be cut from a langasite single crystal. Can be. Therefore, the characteristics of the Y50 wafer itself can be improved, and the production efficiency of the Y50 wafer can be dramatically improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of a method for pulling a langasite single crystal.

FIG. 2 is a perspective view showing the outer shape of a langasite single crystal.

FIG. 3 is an explanatory diagram of a hexagonal crystal structure.

FIG. 4 is an explanatory diagram of the definition of the Y50 plane.

FIG. 5 is a schematic view showing a cut-out portion of a Y50 wafer in a langasite single crystal pulled up in a Z-axis direction.

FIG. 6A is an explanatory diagram showing a state of a hexagonal crystal structure viewed from a Z-axis direction, and FIG. 6B is an explanatory diagram showing a state of a hexagonal crystal structure viewed from a + X-axis direction. .

FIG. 7 is a perspective view showing a seed crystal used in a method of pulling a langasite single crystal pulled in a direction perpendicular to the Y54 plane.

FIG. 8 is a schematic diagram showing a cut-out portion of a Y50 wafer using a langasite single crystal pulled in a direction perpendicular to the Y54 plane.

[Explanation of symbols]

 1 Crucible 5 Pulling shaft, C Langasite single crystal L Melt S Seed crystal

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G077 AA02 BE05 CF10 ED02 EH08 HA11

Claims (2)

[Claims] 1. A seed crystal having the following formula: To produce a langasite single crystal by rotating the seed crystal in a direction perpendicular to the crystal plane while rotating the seed crystal, wherein the seed crystal is pulled while gradually reducing the rotation of the seed crystal in a range of 20 to 2 rpm. A method for pulling a langasite single crystal, comprising: 2. A langasite single crystal produced by the method for pulling a langasite single crystal according to claim 1.