JPH0529866A - Grinding method for ferroelectric substance wafer - Google Patents

Abstract

PURPOSE:To offer the grinding method of a ferroelectric substance where grinding work is accurately executed in short time. CONSTITUTION:A wafer 1 consists of the single crystal of tantalic acid lithium or niobic acid lithium adding Z-axis component in the orientation of a wafer face. In the wafer, grinding speed is different concerning a positive side polarization face + and the negative side polarization face --in spite of relation where the positive side polarization face + and the negative side polarization face -are the surface and back faces of a same thing. The positive polarization faces + have almost same grinding speed with each other and the negative side polarization faces-have almost same grinding speed with each other. The speed of the positive side polarization face f is faster than that of the negative side polarization face. When the plural wafers are simultaneously ground, either of the positive side polarization face + or the negative side polarization face -is arranged so as to simultaneously execute grinding so that grinding work is accurately executed in short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for polishing a ferroelectric wafer which serves as a substrate for a surface acoustic wave device in the field of mobile communication.

[0002]

2. Description of the Related Art In the field of mobile communication such as automobile phones and cordless phones, a ferroelectric wafer obtained from a single crystal of lithium tantalate or lithium niobate is used as a substrate of a surface acoustic wave device.

These surface acoustic wave devices (SAW devices)
The single-crystal ferroelectric wafer used for is manufactured as follows. First, the single crystal obtained by pulling the single crystal is subjected to a polarization operation called single domainization (poling), and at this time, the positive polarity and negative polarity of the Z axis are determined.
The positive polarity here means the side connected to the negative electrode of the DC voltage applied by poling, and the negative polarity means the side connected to the positive electrode. A wafer is obtained by slicing the polarized short crystal body. One surface of this wafer is mirror-polished, and the other surface is roughened to form a ferroelectric wafer.

The polishing process is performed by sticking a considerable number, for example, several tens of sheets onto one glass plate in order to maintain the uniformity of the thickness after polishing and improve the working efficiency. Whether the surface to be polished is a positive polarization surface or a negative polarization surface does not cause a problem in terms of device characteristics as a surface acoustic wave element. Therefore, it is completely unaware of which surface, the positive-side polarized surface or the negative-side polarized surface, is processed into a mirror surface.
In fact, the two were mixed together and then attached to the glass plate and polished together.

[0005]

In the conventional polishing process described above, the polishing rate for each polishing batch may vary greatly. Since the polishing amount of the wafer varies depending on the polishing batch even if the polishing time is constant, it was necessary to frequently interrupt the polishing during the polishing to measure the thickness of the wafer. As described above, there is a problem that productivity is poor because the working time other than the actual polishing time is long, which causes an increase in processing cost, and the thickness of the obtained wafer also varies widely.

In order to solve such a problem, the present invention intends to provide a method for polishing a ferroelectric wafer, which is capable of efficiently performing a polishing process in a short time and obtaining an accurate wafer. .

[0007]

In order to solve the above-mentioned problems of the conventional method of polishing a ferroelectric wafer, the inventor of the present invention uses a single layer of a ferroelectric wafer, especially lithium tantalate or lithium niobate. The polishing rate of a crystal wafer was studied. First, it was predicted that there was some relationship between the Z-axis polarity of these single crystal wafers and the polishing rate, and several cut faces containing the Z-axis component in the plane orientation were made and a polishing test was conducted. As a result, it has been found that the polishing rate is different between the positive and negative polarization surfaces, even though the positive and negative polarization surfaces are the same. Further, it has been found that when a plurality of ferroelectric wafers are made of the same material, the positive-polarized surfaces have almost the same polishing rate, and the negative-polarized surfaces have almost the same polishing rate. The positively polarized surface has a higher polishing rate than the negatively polarized surface, and may be about twice as fast depending on the material and polishing conditions.

The structure of the present invention made by paying attention to the polishing characteristics of such a ferroelectric wafer has a Z-direction in the wafer plane direction.
In the method of simultaneously polishing a plurality of wafers composed of a single crystal of lithium tantalate or lithium niobate containing an axial component, a plurality of wafers polarized on the front and back in the thickness direction are either positive-polarized surfaces or negative-polarized surfaces. This is a method for polishing a ferroelectric wafer, which is characterized by aligning on one side and polishing simultaneously.

In this polishing method, it is possible to polish the positive polarization surface in a shorter time.

The wafer is a Z-cut plate and a rotating Y-cut plate. More specifically, the wafer is a 36 ° rotated Y-cut lithium tantalate single crystal or a 64 ° rotated Y-cut lithium niobate single crystal.

[0011]

As described above, in a plurality of ferroelectric wafers, the positive-polarized surfaces have almost the same polishing rate, and the negative-polarized surfaces have almost the same polishing rate.
By simultaneously polishing a plurality of wafers by aligning either the positive-side polarized surface or the negative-side polarized surface at the same time, the load applied to the polished surface becomes uniform, and each wafer is polished at the same speed.

If the positive-side polarized surface is polished, the positive-side polarized surface has a higher polishing rate than the negative-side polarized surface, so that faster polishing is possible.

[0013]

EXAMPLES Examples of a method of polishing a ferroelectric wafer to which the present invention is applied will be described in detail below.

The material of the ferroelectric wafer to be polished is a Z-axis positive electrode obtained by polarizing a 3-inch thick rod-shaped single crystal obtained by pulling a single crystal from a melt of lithium tantalate or lithium niobate. It is obtained by slicing the negative polarity and the negative polarity. It should be noted that the orientation of the wafer flat surface obtained by slicing orientation flats at two locations, large and small, on the outer periphery of the round rod-shaped single crystal at an angle of 90 degrees and slicing at the orientation flats The negative polarity surface was identified. Then both sides of this material # 20
Lapping with 00 silicon carbide abrasive grains to a thickness of 400
μm, parallelism was finished to 1 μm.

This wafer was mirror-polished by the following procedure. As shown in FIG. 1, the wafer 1 has all the positive-side polarized surfaces + aligned with the upper surface as polishing surfaces, or all the negative-polarized surfaces − aligned with the upper surface as polishing surfaces, based on the orientation flat a. Wax is applied on the plate 2 in batches of 30 sheets. The polishing surface was polished by a rotary polishing machine to obtain a ferroelectric wafer. Polyurethane impregnated polyester non-woven fabric is used as the polishing cloth, colloidal silica is used as the polishing liquid,
A surface pressure of 200 g / cm ² was applied.

The samples of Examples 1 to 6 shown in Table 1 were actually polished according to the above procedure, the polishing rate and the parallelism of the wafer were measured, and the average value thereof was calculated.

Regarding the samples of Comparative Examples 1 to 3 in Table 1, the 30 wafers 1 having the positive polarization surface + facing upward and the negative polarization surface − facing upward are described in the table. The same polishing was performed by mixing the same number of wafers, and the polishing rate and the parallelism of the wafer were calculated. The polishing rate was calculated from the time required to polish a thickness of 15 μm. The parallelism of the wafer is the difference between the maximum and minimum measured thicknesses at 5 points in the polished wafer surface.

[0018]

[Table 1]

[0019]

As described in detail above, according to the method for polishing a ferroelectric wafer of the present invention, when polishing a plurality of wafers at the same time, the surface having a uniform polishing rate is polished. The load becomes uniform, and the wafer is polished with no variation in wall thickness, and the processing accuracy of the wafer is improved.
In particular, if the polishing surface is uniformly specified as the positive polarization surface side, the polishing process time can be greatly shortened. Further, variations in polishing rate between batches are reduced, and time control of polishing stock removal is facilitated. In addition, this makes it possible to reduce the processing cost and improve the productivity.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the middle of the steps of a polishing method to which the present invention is applied.

[Explanation of symbols]

1 ... Wafer, 2 ... Glass plate.

Claims (5)

[Claims] 1. A method for polishing a wafer cut out from a single crystal of lithium tantalate or lithium niobate which is polarized in a coaxial direction and includes a Z-axis component in a wafer plane orientation, and is polarized in the thickness direction. A method of polishing a ferroelectric wafer, which comprises polishing the wafer by aligning the polarization direction of the wafer with one of the positive polarization surface and the negative polarization surface. 2. A method of polishing a ferroelectric wafer, which comprises polishing the wafer so that the polarization direction of the wafer is aligned with the positive polarization surface. 3. The method for polishing a ferroelectric wafer according to claim 1, wherein the wafer is a Z-cut plate and a rotating Y-cut plate. 4. The method for polishing a ferroelectric wafer according to claim 1, wherein the wafer is a 36 ° rotated Y-cut lithium tantalate single crystal. 5. The method for polishing a ferroelectric wafer according to claim 1, wherein the wafer is a 64 ° rotated Y-cut lithium niobate single crystal.