JP2000082931A - Piezoelectric single crystal wafer, its manufacture and surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave device superior in electric characteristics and to supply a highly precise device by removing a machined distorted layer consisting of a crack layer and an elastic distortion layer on the surface of a piezoelectric single crystal wafer. SOLUTION: A piezoelectric single crystal wafer 1, a crack layer 2, a, elastic distorted layer 3, a machined layer 4 and a mirror polishing area 5 are displayed. In such a case, the wafer where the machined distorted layer 4 of the crack layer 2 and the elastic distortion layer 3 does not exist is obtained on the surface of the electrode forming face-side of the piezoelectric single crystal wafer (wafer) 1. Thus, the wafer 1 is etched and the thickness D/3 being at least 1/3 of the thickness D of the crack layer is polished in addition to the thickness D of the crack layer of the wafer 1 by using abrasive grains whose average grain diameter is not more than 100 nm and using abrasive cloth having raised fibers (nap). Namely, the mirror area 5 with 4/3D in the thickness of the crack layer is mirror-polished and the surface of the wafer 1 is finished.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric single crystal wafer used for a substrate of a surface acoustic wave device or the like and a method for manufacturing the same.

In general, a single crystal wafer of lithium niobate or lithium tantalate is used as a piezoelectric substrate of a surface acoustic wave (SAW) filter used in a television picture medium frequency (TV-IF) filter or a mobile phone filter.

[0003] In recent years, in order to improve the characteristics of these filters, various surface treatments such as etching and mirror finishing have been performed in order to remove processing distortion during lapping of a single crystal.

[0004]

2. Description of the Related Art FIG. 1 is an explanatory view of a strained layer caused by lapping of a wafer and a mirror-polished region.

In the drawing, reference numeral 1 denotes a piezoelectric single crystal wafer, 2
Is a crack layer, 3 is an elastic strain layer, 4 is a work strain layer, and 5 is a mirror-polished region. 2. Description of the Related Art Conventionally, piezoelectric single crystal wafers used for surface acoustic wave devices and the like often use piezoelectric single crystals. In the production of a piezoelectric single crystal wafer, a single crystal ingot that has been annealed and poled is sliced into a wafer by a wire saw or an inner peripheral blade, and then double-sided lapping is performed using silicon carbide (SiC) -based abrasive grains.

[0006] As shown in FIG. 1, on the surface of a double-sided wrapped piezoelectric single crystal wafer (hereinafter referred to as a wafer) 1, a processing strain layer 4 comprising a crack layer 2 and an elastic strain layer 3
Exists. Therefore, after the processing strain layer 4 is removed to some extent by etching, the surface of the wafer 1 on which the electrode pattern is formed is mirror-finished.

[0007]

Conventionally, the above-mentioned etching conditions and mirror polishing amount have been set so that no cracks remain on the wafer surface after the mirror surface processing. And other piezoelectric substrates.

However, even if a mirror-surface wafer having no cracks on the surface is visually observed, if elastic strain that cannot be seen remains, for example, when a surface acoustic wave device or the like is manufactured using the wafer as a substrate, electrical characteristics deteriorate. Is recognized.

This is because, for example, in a surface acoustic wave device, the surface acoustic wave propagates on the very surface of the wafer.
It is considered that surface acoustic waves are attenuated due to processing strain.

[0010] An object of the present application is to solve the above-mentioned problems and to provide a piezoelectric single crystal wafer free of cracks and processing distortion.

[0011]

FIG. 1 is a sectional view of a wafer showing a strained layer on the surface of the wafer by lapping.

In the figure, 1 is a piezoelectric single crystal wafer, 2
Is a crack layer, 3 is an elastic strain layer, 4 is a work strain layer, and 5 is a mirror-polished region. In the present invention, as shown in FIG. 1, a wafer is obtained in which a processing strain layer 4 composed of a crack layer 2 and an elastic strain layer 3 does not exist on the surface on the electrode forming surface side of a piezoelectric single crystal wafer (hereinafter, wafer) 1.

For this purpose, after the wafer 1 has been subjected to the etching treatment, polishing abrasive grains having an average particle diameter of 100 nm or less are used, and a polishing cloth 7 having a nap 6 as shown in FIG. Then, in addition to the crack layer thickness D of the wafer 1 shown in FIG. 1, at least one third of the crack layer thickness D D / 3 is polished, that is, the crack layer thickness is reduced. The 4 / 3D mirror polishing region 5 is mirror-polished to finish the surface of the wafer 1.

According to the surface finishing method of the present invention, not only the crack layer on the wafer surface but also the elastic strain layer can be completely removed, so that a wafer without processing distortion can be manufactured. Using such a wafer, a piezoelectric single crystal wafer such as a surface acoustic wave device having excellent electrical characteristics can be manufactured.

[0015]

FIG. 3 is an explanatory diagram of SAW band-pass filter characteristics. FIG. 4 is an explanatory diagram of the 800 MHz band SAW bandpass filter characteristics.

In the present invention, as one embodiment, a wafer processing method when a piezoelectric single crystal wafer is used as a substrate of a surface acoustic wave device will be described. As a sample, 4
A lithium tantalate (LiTaO ₃ ) single crystal wafer with 0 ° rotation Y was used. This single crystal produced by the Czochralski (CZ) method was sliced with a wire saw, and then double-sided lapping was performed using FO # 1000 abrasive grains. At room temperature, a mixed solution of hydrofluoric acid and nitric acid (HF: HN
Etching was performed in O ₃ = 1: 2) for 1 hour.

Next, colloidal silica abrasive grains having an average particle size of 80 nm are used to reduce processing distortion due to mirror polishing and to obtain surface roughness required for forming electrodes. Using a polishing cloth having a nap as shown in No. 2, the surface of the wafer was mirror-polished to a thickness of 10 to 20 μm.

Then, aluminum (Al) is formed on the mirror-finished surface of each wafer by DC sputtering.
A film was formed, and the surface of the Al film was inspected using a dark field of a metal microscope.

As a result, cracks having a size of several μm were observed on the entire surface of the wafer after mirror polishing to a thickness of 10 to 14 μm, but no cracks could be confirmed in a wafer polished to 15 μm or more. Was. From this observation result, it was found that the thickness of the crack layer was 15 μm.

Next, using the above wafer, 800M
A SAW (surface acoustic wave) bandpass filter in the Hz band was manufactured. The evaluation of the characteristics of the bandpass filter was confirmed using the minimum insertion loss as shown in FIG. FIG. 4 shows the relationship between the mirror polishing amount and the minimum insertion loss of the SAW bandpass filter.

As shown in FIG. 4, as the mirror polishing amount increases, the minimum insertion loss of the SAW filter decreases, and the crack layer thickness of the wafer is 15 μm and the crack layer thickness is 1 μm. It can be seen that if 5 μm of ３ is additionally polished and mirror polishing of 20 μm is performed, a constant value is shown beyond that.

From the above results, it is possible to remove not only the crack layer but also the elastic strain layer by mirror-polishing at least one third of the thickness of the crack layer after removing the crack layer of the wafer. S with low minimum insertion loss
An AW bandpass filter can be manufactured.

Such a piezoelectric single crystal wafer can be used as a substrate for various filters, oscillators, delay lines (delay lines), convolvers, pressure sensors, and the like.

[0024]

As described above, according to the present invention,
By fully etching the wafer surface with a mixture of nitric acid and hydrofluoric acid and completely removing the crack layer and the elastic strain layer on the wafer surface by mirror polishing, a surface acoustic wave device with excellent electrical characteristics is obtained. And a more accurate device can be supplied.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a work-strained layer and a mirror-polished region due to lapping of a wafer

FIG. 2 is a sectional view of a polishing cloth used for mirror polishing according to the present invention.

FIG. 3 is an explanatory diagram of SAW bandpass filter characteristics.

FIG. 4 is an explanatory diagram of characteristics of an 800 MHz band SAW bandpass filter.

[Explanation of symbols]

 In the figure, 1 a piezoelectric single crystal wafer 2 a crack layer 3 an elastic strain layer 4 a work strain layer 5 a mirror polished area 6 a napping 7 (nap) 7 a polishing cloth

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Claims (8)

[Claims] 1. A piezoelectric single crystal wafer characterized in that a cracked layer and a processing strain layer comprising an elastic strain layer on the surface of the piezoelectric single crystal wafer are removed. 2. The piezoelectric single crystal wafer according to claim 1, wherein at least 4/3 of the thickness of the crack layer on the surface of the wafer is polished. 3. A method for manufacturing a piezoelectric single crystal wafer, comprising: after etching a surface of a piezoelectric single crystal wafer, removing a work-strained layer comprising a crack layer and an elastic strain layer by mirror polishing. 4. The method for producing a piezoelectric single crystal wafer according to claim 3, wherein at least 4/3 of the thickness of the crack layer on the wafer surface is mirror-polished. 5. The method for producing a piezoelectric single crystal wafer according to claim 3, wherein a polishing cloth having raised fibers is used for the mirror polishing. 6. The method for manufacturing a piezoelectric single crystal wafer according to claim 3, wherein abrasive grains having a diameter of 100 nm or less are used for the mirror polishing. 7. The method according to claim 3, wherein the wafer is made of lithium tantalate. 8. A surface acoustic wave device comprising the piezoelectric single crystal wafer according to claim 1 as a substrate.