JPH04285025A - Single domainization method for piezoelectric single crystals - Google Patents

Abstract

PURPOSE:To obtain a wafer hardly warped in spite of its large diameter by polarizing a ferroelectric piezoelectric single crystal in an electric field applied with the pulling direction side negatively. CONSTITUTION:Pt electrodes 2 are fitted to a ferroelectric piezoelectric single crystal 4 with ceramic powder 3 in-between and the crystal 4 is heated to the Curie temp. or above and cooled in a DC electric field. The crystal 4 is polarized in the electric field applied with the pulling direction side negatively.

Description

[Detailed description of the invention]

[Object of the invention]

0002

[Field of Industrial Application] The present invention relates to a method for forming a ferroelectric piezoelectric single crystal into a single region, and more particularly, to a method for forming a ferroelectric piezoelectric single crystal into a single region, and in particular to a method for processing a ferroelectric piezoelectric single crystal using a loose abrasive processing device such as a wire saw. Concerning a method for dividing into one domain.

0003

[Prior Art] Conventionally, LiNbO 3 and LiTaO
Ferroelectric piezoelectric single crystals such as No. 3 need to be made into a single domain, so the temperature is raised above the Curie temperature and the cooling operation is performed under a DC electric field as shown in FIG. Single crystals that are not subjected to single-segmentation treatment become more susceptible to cracking. However, at this time, no particular distinction was made between the direction of single crystal growth and the direction of the applied electric field. However, when single-segmenting treatment is performed with the pulling direction side of the ferroelectric piezoelectric single crystal as the positive side, the single crystal often becomes colored or easily cracked. Furthermore, recently, in order to increase the yield during wafer manufacturing of these piezoelectric single crystals, free abrasive processing methods such as a wire saw, which cause less processing distortion, have been increasingly used. In addition, as the diameter of wafers progresses from 3" to 4", the problem of straightness, which is a drawback of wire saws, becomes more difficult, and it becomes difficult to maintain the accuracy of wire saws. Ta.

0004

[Problem to be solved by the invention] LiNbO 3 and L
A ferroelectric piezoelectric single crystal such as iTaO 3 has cleavability and is easily broken. Therefore, even if the free abrasive processing method has low processing distortion, if the slicing accuracy is poor,
In the next process of lapping and SAW substrates, cracks often occur due to localized stress being applied during honing of the back surface. In addition, as the diameter of wafers increased, such as 4", the straightness worsened, leading to a decrease in yield during wafer manufacturing. To improve the straightness, it was necessary to slow down the slicing speed and The running cost is high and the ferroelectric piezoelectric single crystal must be replaced quickly, making it extremely inefficient.The purpose of the present invention is to provide an efficient method for slicing a ferroelectric piezoelectric single crystal that has good elongation even with a large diameter. [Structure of the invention]

[0005]

[Means for Solving the Problems] The present invention provides a method for dividing a ferroelectric piezoelectric single crystal into a single crystal by heating the ferroelectric piezoelectric single crystal to a temperature higher than the Curie temperature and cooling the ferroelectric piezoelectric single crystal under a DC electric field. In this method, the ferroelectric piezoelectric single crystal is polarized with the pulling direction side of the ferroelectric piezoelectric single crystal set in a negative direction in the electric field application direction during the polarization process. The ferroelectric piezoelectric single crystal contains LiNbO 3
, LiTaO 3 , etc., but LiTaO 3 is preferable for the present invention.

As shown in FIG. 1, the polarization treatment of a ferroelectric piezoelectric single crystal is carried out with the pulling direction side of the single crystal being negative in the direction in which the electric field is applied during the polarization treatment. The method of applying the DC electric field is
There is no particular restriction as long as the negative electrode is on the pulling direction side of the single crystal.

[0007]

[Operation] The shape of the solid-liquid interface formed during the growth of LiNbO 3 or LiTaO 3 is generally downwardly convex. When cutting with a wire saw, the wire is thin and has poor straightness, and the shape of the slice is affected by the shape of the solid-liquid interface and similarly becomes convex downward. However, by setting the electric field application direction during the polarization treatment so that the pulling direction side of the single crystal is negative, the seed of the growth axis becomes a surface having a positive polar component. As a result, the downwardly convex cut surface is corrected to the negative side with lower hardness, resulting in less warpage and a wafer with good flatness. Furthermore, when lapping the cut wafer, the contact area of the positive side increases as shown in FIG. 3, so the processing time becomes faster. After wrapping, take a look at the negative aspects.
Even after lapping, the direction of the warp that remains after lapping remains the same and the warp does not reverse, which reduces the occurrence of cracks in the wafer. When performing hydrofluoric acid-nitric acid etching to correct large warpage after honing, the warpage that remains after lapping is in the same direction, so the warpage does not reverse. In addition, warpage can be easily controlled.

[0008]

[Examples] Examples of the present invention will be described below.

Example 1 Raised 128° Y axis 4”Ф x 100
LiNbO 3 in mm L LiNbO 3 single crystal
Sprinkle ceramic powder, attach a Pt electrode on top of it,
It was slowly heated to 1150° C. or higher, and slowly cooled by applying 25 V as a negative voltage component to the pulling side and 25 V as a positive voltage component to the bottom side.

[0010] The orientation of the bottom side of this LiNbO 3 single crystal was measured, and the bottom was processed using a processing machine. Next, rounding is performed and orientation flats are processed. This ball is adhered to a single crystal mounting table using an organic adhesive and placed in a cutting device. Wrap the wire around the three rollers and align the crystal end face with the wire. GC#1200 slurry was uniformly poured from the center. Then slowly wire
was sent out and cutting started. After 20 hours, the crystal was removed from the wire while being washed with kerosene, and immersed in an adhesive stripping solution to obtain a wafer.

[0011] When the warpage of the cut wafers was measured, all of the warpages were 20 μm or less.

[0012] Also in the direction of warpage, the positive side was concave. Further, when this wafer was lapped, the positive surface had a concave warp of 10 μm or less. Next, the negative side of this wafer was honed to a roughness of Ra~2.5 or more. At this time, the positive side has a concave warp of 60μ
It was m. When this wafer was etched with hydrofluoric acid-nitric acid, the warp was corrected to 10 μm. Thereafter, the positive surface was mirror-polished and etched with hydrofluoric acid-nitric acid, and the positive surface was corrected to a concave warp of 8 μm.

Embodiment 2 Raised Z axis 4 ”Ф x 100 mm L
LiTaO 3 ceramic powder is applied to the LiNbO 3 single crystal of 1150
Heat slowly to above ℃, and apply 25V as a negative voltage component on the pulling side and 25V as a positive voltage component on the bottom side.
V was applied and the mixture was slowly cooled.

[0014] The orientation of the bottom side of this LiNbO 3 single crystal was measured, and the bottom part was processed using a processing machine. Next, rounding is performed and orientation flats are processed. This ball is adhered to a single crystal mounting table using an organic adhesive and placed in a cutting device. Wrap the wire around the three rollers and align the crystal end face with the wire. GC#1200 slurry was uniformly poured from the center. Then slowly wire
was sent out and cutting started. After 20 hours, the crystal was removed from the wire while being washed with kerosene, and immersed in an adhesive stripping solution to obtain a wafer.

When the warpage of the cut wafers was measured, all of the warpages were 20 μm or less.

[0016] Also in the direction of warpage, the positive side was concave. Further, when this wafer was lapped, the positive surface had a concave warp of 10 μm or less. Next, the negative side of this wafer was honed to a roughness of Ra~2.5 or more. At this time, the positive side has a concave warp of 60
It was μm. When this wafer was etched with hydrofluoric acid-nitric acid, the warp was corrected to 12 μm. Thereafter, the positive surface was mirror-polished and etched with hydrofluoric acid-nitric acid, and the positive surface was corrected to a concave warp of 8 μm.

Example 3 Raised 36° Y axis 3”Ф x 100 mm
A on the pulled part and bottom of the LiTaO 3 single crystal of L
Attach G paste as an electrode, heat slowly to 750℃ or higher, and apply 80℃ as a negative voltage component to the pulling side.
A positive voltage component of 80 V was applied to the bottom side of the sample to slowly cool it down. The orientation of the bottom side of this LiTaO 3 single crystal was measured, and the bottom was processed using a processing machine. Next, rounding is performed and orientation flats are processed. This ball is adhered to a single crystal mounting table using an organic adhesive and placed in a cutting device. Wrap the wire around the three rollers and align the crystal end face with the wire. GC#1200 from the center
The slurry was poured uniformly. After that, the wire was slowly fed out and cutting started. After 20 hours, the crystal was removed from the wire while being washed with kerosene, and immersed in an adhesive stripping solution to obtain a wafer.

When the warpage of the cut wafers was measured, all of the warpages were 15 μm or less.

[0019] Also in the direction of warpage, the positive side was concave. Furthermore, when this wafer was lapped, the positive surface had a concave warp of less than 8 μm. Next, the negative side of this wafer was honed to a roughness of Ra~1.5 or more. At this time, the positive side has a concave warp of 30μ
It was m. When this wafer was etched with hydrofluoric acid-nitric acid, the warp was corrected to 7 μm. Thereafter, the positive surface was mirror-polished and etched with hydrofluoric acid-nitric acid, and the positive surface was corrected to a concave warp of 6 μm.

Comparative Example Raised 128° Y-axis 4”Ф x 100
LiNbO 3 in mm L LiNbO 3 single crystal
Sprinkle ceramic powder, attach a Pt electrode on top of it,
It was slowly heated to 1150° C. or higher, and slowly cooled by applying 25 V as a negative voltage component to the bottom side and 25 V as a positive voltage component to the pulling side. This LiNbO
3. The orientation of the bottom side of the single crystal was measured, and the bottom was processed using a processing machine. Next, rounding is performed and orientation flats are processed. This ball is adhered to a single crystal mounting table using an organic adhesive and placed in a cutting device. Wrap the wire around the three rollers and align the crystal end face with the wire. GC#1200 slurry was uniformly poured from the center. After that, the wire was slowly fed out and cutting started. After 20 hours, the crystal was removed from the wire while being washed with kerosene, and immersed in an adhesive stripping solution to obtain a wafer.

When the warpage of this cut wafer was measured, it was found to be less than 70 μm. In the direction of warpage, the positive side was convex. Further, when this wafer was lapped, the positive surface had a convex warp of 40 μm or less. Next, the negative side of this wafer was honed to a roughness of Ra~2.5 or more. At this time, the positive side had a concave warp of 60 μm. When this wafer was etched with hydrofluoric acid and nitric acid, the etching rate was 40% in 1 minute.
The warpage was corrected to μm. After this, the positive side was polished to a mirror finish, and the wafer, which had a warp of 80 μm, was exposed to hydrofluoric acid.
When etched with nitric acid, the 40 μm positive surface was corrected to a convex warp. The polishing yield at this time is 70%
It got worse.

[0022]

[Effects of the Invention] As is clear from the above embodiments, the present invention can produce wafers with extremely low warpage of 10 μm or less with a high yield even for large diameter ferroelectric piezoelectric single crystal wafers for surface acoustic waves of 4”Ф. Can be manufactured.

[Brief explanation of the drawing]

FIG. 1: 128° Y-axis LiNbO 3 according to the present invention
We show a single domainization method.

FIG. 2 shows a conventional 128° Y-axis LiNbO 3 single domainization method.

FIG. 3 shows a diagram of double-sided lapping.

[Explanation of symbols]

1...seed 2...Pt electrode 3...Ceramics powder 4...Crystal 5...Wafer 6...Career 7... Negative aspects 8...Positive side

Claims (2)

[Claims] Claim 1. A method for dividing a ferroelectric piezoelectric single crystal into a single domain by heating the ferroelectric piezoelectric single crystal to a temperature higher than the Curie temperature and cooling the ferroelectric piezoelectric single crystal under a direct current electric field. A method for making a ferroelectric piezoelectric single crystal into a single domain, characterized in that the pulling direction side of the piezoelectric single crystal is polarized with the electric field application direction during the polarization treatment being negative. [Claim 2] The ferroelectric piezoelectric single crystal is LiNbO 3
2. The method for dividing a ferroelectric piezoelectric single crystal into a single domain according to claim 1, wherein the ferroelectric piezoelectric single crystal is a single crystal.