JPS58167496A - Preparation of wafer of lithium tantalate single crystal - Google Patents

Abstract

PURPOSE:To obtain a wafer having no propagation attenuation of surface accoustic wave, by growing lithium tantalate single crystal using a seed crystal having a crystallographical orientation in a direction with a specific angle from Y axis, allowing it to form single domains, taking it out perpendicularly to a pulling axis. CONSTITUTION:A lithium tantalate seed crystal having a crystallographical orientation with a gradient of 36 10 degrees from y axis in the z axis direction is prepared. The seed crystal is immersed in lithium tantalate melt formed in a crucible, it is pulled up gradually in a crystallographical orientation in the direction of 36 10 degrees from Y axis, to grow it into a given thickness and length. The electrodes 3 are set above and below the pulling axis of the prepared single crystal 1'' grown in the direction of 36 10 degrees from y axis, and DC voltage is applied to them so that it is allowed to form single domains. The single crystal 1'' is taken out approximately perpendicularly to the pulling axis, to give a round-shaped wafer having a plane orientation in the direction of 36 10 degrees from Y axis.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a 36°±10@Y lithium tantalate single crystal.
This invention relates to a method of manufacturing a wafer having an axial surface orientation.

Lithium tantalate (LiTaO single crystal) is used in IP filters for TV receivers, etc.

As a new application, research is also being conducted into 8-W (surface acoustic wave) filters and sensors for communication devices such as car phones. For the Tv receiver/receiver suspension, an X-plate thread (plane orientation <2TO>) cut from an X-axis pulled single crystal among lithium tantalate single crystals is used.

On the other hand, for application to 8AW filters for car phones, wafers with s6@±10'' Y-axis orientation are considered promising due to their properties, and currently tutium tantalate single crystal wafers with this orientation are being developed. 1. For example, as shown in Fig. 1, an X-axis pulled single crystal 1 is cut out vertically along cutting line 2 at 36°±1.
Attempts have been made to obtain a wafer having a surface orientation in the 0'Y-axis direction. However, when using this method, the shape of the wafer becomes a square. The size will be uneven. There is a disadvantage that the utilization efficiency of the single crystal (the yield when cutting into quay) is poor.

On the other hand, as shown in FIG. 2, by diagonally cutting out the Y-axis (<010>) or Z-axis (<001>) pulled single crystal 1' along the cutting line 2, the same process as in FIG. Attempts have also been made to obtain wafers with the same plane orientation, but in this case as well, the disadvantage is that the utilization efficiency of the single crystal is poor, and the elliptical shape of the wafer makes it difficult to handle in the device manufacturing process. There is.

The present invention solves this disadvantage, and the distance is 340±lθ from the Y-axis toward the Z-axis direction.

using a seed crystal with a crystallographic orientation of inclination of 36°
A process of forming a lithium tantalate single crystal in the ±106 Y-axis direction, a process of dividing the obtained single crystal into a single domain, and a round wafer having a plane orientation of 36° + 10' Y-axis direction from this single crystal. The present invention relates to a method for manufacturing a tutsicum tantalate single crystal wafer, which comprises a step of cutting out substantially perpendicular to the Y-pulling axis.

According to the method of the present invention, 1) it is possible to easily obtain round wafers, 2) it is easy to inspect and correct the plane orientation during cutting, 2) the crystal utilization efficiency is significantly improved, and 2) it has a constant shape. The advantage of using this method for round quays is to improve the efficiency of the 8AW device manufacturing process. In particular, this advantage (2) increases as the diameter (Quey diameter) of the pulled single crystal increases.

The method of the present invention will be explained in detail below.

First, in advance, 36＠±1 from the Y axis in the two-axis direction.
A seed crystal having a crystallographic orientation with an inclination of 0' is prepared, for example, by pulling it in the X-axis direction or cutting it perpendicular to the Y-axis or the bezel (Weh 8) using a conventional method. Alternatively, it is possible to use a section cut out in the direction of the pulling axis from a single crystal pulled by the method of the present invention as shown in Figure s3.

This seed crystal is formed in an iridium crucible or immersed in a y-talate melt, and is gradually pulled up in the crystal engineering direction of the 3610 Y-axis direction, thereby growing to a desired thickness and length. As a means for heating the raw material melt, a high-pitched wave induction heating device may normally be used. 36°+: lO°
When pulled up to the Y-axis range, the (<012>) plane, which is the open plane of the Li Ta Os single crystal, becomes almost perpendicular to the pulling axis (
32.9° (perpendicular in the case of the Y-axis), and since the stem 1 of the crystal itself acts on the (<012>) plane as a tensile stress, cracks at the (<012>) plane cause seeds and crystals to form. Occur and belong. In order to prevent cracks on this (<012>) plane, it is necessary to minimize the temperature difference in the pulling axis direction and radial direction of 11 and the crystal during cooling, so that the upper end of the seed is in the heat-insulating cylinder during cooling. It is preferable to keep the heat insulating tube higher than the conventional heat insulating tube so that it does not escape outside, and to cool the seeds with the seeds inside the insulating tube. Alternatively, a mixture of (10 oxygen in an inert gas) may be used, but it is preferable to conduct the foreman in a mixed gas of an inert gas and oxygen to prevent cracking, and to keep an atmosphere containing oxygen during cooling. It is desirable to keep the

Next, the crystal grown in this way is made into a single domain in the next step. The specific method of this single area division is shown in Figure 4.
As shown in No. sH. That is, as shown in Fig. 114, electrodes (Pt electrodes) 8 are set above and below the pulling axis direction of the 36° ± 10 @ Y glaze direction sensitive length single crystal 1', or as shown in Figs. 5 (A) and (B). The electrode (Pi
Single segmentation is easily performed by setting the electrodes and applying a DC voltage, and the applied power at this time is
m.

There is no need to apply an applied electric field in the Z-axis direction, and the single domain can be successfully achieved by the above method. .

Note that the method for achieving this single area is the method previously proposed by the present inventors, in which a pair of electrode plates are placed in a treatment tank made of heat insulating material and spaced so that their surfaces are parallel to each other. The single crystal 1' is arranged approximately in the center between the electrode plates, the treatment tank is densely filled with powder of the same type as the single crystal, and a DC voltage is applied to the electrode plates. The method is also advantageously employed.

Next, the single crystal that has been made into a single domain as described above is cut out almost perpendicularly to the pulling axis, and thereby sr+lo°Y
To obtain a round wafer with an axial surface orientation,
At this time, the reference plane is the (<ox2>) plane or it (<
It is preferable to orient these images with X-rays using the 014>) plane, and then rotate them by a predetermined angle using the X-axis as the rotation axis.

Note that although the 36°+109 Y-axis direction is used as the azimuth, naturally the present invention also covers an azimuth 180° opposite to these azimuths.

As explained above, according to the method of the present invention, as shown in the third factor, by simply cutting out the lithium tantalate single crystal perpendicular to the single crystal pulling direction, the desired lithium tantalate single crystal with a plane orientation of 366±10e in the Y-axis direction can be obtained. The wafers can be obtained as products with consistent quality and uniform characteristics at a high yield.

The lithium tantalate single-crystal wafer obtained in this way has the characteristic that the propagation attenuation of surface acoustic waves is almost zero because its surface orientation is 36° earth 1OOY axis direction, and furthermore, the temperature characteristics are small. ing.

Next, the specific ratio IIR4P11. Yage money for example.

Comparative Example 1 [111too] 3700P of unsintered tantalate powder was put into an iridium crucible with a height of 100mm, and this was melted using a high-frequency induction heating device.

Dip the lithium tantalate seed crystal on the Y axis into this, and
3 ■ A tantalum steep lithium single crystal with a length of about 100-
, +3.0 capacity%0. ) After the growth was completed, the crucible was cooled to 100% nitrogen atmosphere to protect the crucible, and then removed from the apparatus.

After the obtained single crystal is oriented and cut into single domains.

It was processed into a cylindrical shape with a length of 1.50 mm and a length of 8100 mm.

This cylindrical single crystal is rotated in the 2-axis direction with the X axis as the rotation axis.
After 66 rotations, the wafer is cut out to a thickness of 0.
．． Forty-seven 5- oval wafers were obtained. This was processed into a round shape to obtain the same number of round wafers (plane orientation 36° Y axis) each having a diameter of 50 m and a thickness of 0.5 mm.

Actual Example J1 Comparative Example 1yoot of lithium tantalate powder sintering raw material was put into a #111m crucible and melted in 8 ways. 3@ for this
A lithium tantalate seed crystal oriented in the 0Y-axis direction was immersed, and a lithium tantalate single crystal with a diameter of about s3 and a length of about 100 was made 5 m higher than the comparative example.
, +3.0 volume% O,) was raised in a feces atmosphere, and after the lengthening was completed, the seeds entered the heat-insulating cylinder at a temperature of 0. The obtained single crystal V was taken out from the cooled after-cooling unit. The obtained single crystal V The cage was turned 3.16 times 8 times in the opposite direction and cut in the azimuth direction.Then, the single-segmented cage was processed into a cylindrical shape with a diameter So and a length of 100 mm.By cutting this cylindrical single crystal perpendicularly, a diameter of 15 o-thickness was obtained. 0.5- round wafer (plane orientation 36
83 pieces of glaze (°Y glaze) were obtained.

[Brief explanation of the drawing]

Figures 111 and 2 are diagrams of conventional wafers cut out, Figure 3 is an explanatory diagram of the wafer of the present invention cut out, and Figures 4 and 185 are diagrams of the wafer cut into single crystals of the present invention. This figure shows an explanatory diagram for regionalization. 1, l', l'...single crystal 2...cutting line 8...electrode. Patent Applicant Shin-Etsu Chemical Co., Ltd. Figure 1 Figure 2 × Figure 5 (B) Procedural Amendment April 1981 411 Director-General of the Revision Agency Kazuo Wakasugi 1,! Display of extracts 1983 Patent No. 111'150481 2 Name of the invention Method for producing lithium tantalate single crystal waeno 3 Relationship with the person making the amendment Name of Patent No. 16 applicant (206) Shin-Etsu Chemical Co., Ltd. 4 , Agent 6, Subject of amendment l) Delete "(Ueno\)" in the bottom line of page 4 of Specification IIF. 2) Correct [applied force] in line i & f on page 6 of the specification to "apply magnetic pressure" @

Claims (1)

[Claims] 1. 36° from the Y axis towards the Z axis direction! 36'+ using a seed crystal with a crystallographic orientation with a tilt of lO°
106 A step of growing a lithium tantalate single crystal in the Y-axis direction, a step of dividing the obtained single crystal into a single domain, and a round wafer having a plane orientation of 36°±lO° in the Y-axis direction from this single crystal. A method for manufacturing tantalum lithium single crystal wafers, which comprises a step of cutting out almost perpendicular to the pulling axis.