JP3254685B2 - Method for producing lithium niobate single crystal substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a lithium niobate single crystal substrate for optical use such as an optical waveguide or a surface acoustic wave filter.

[0002]

BACKGROUND ART Lithium niobate single crystal substrate, for example, cut with inner diameter blade cutting machine or a wire saw a single crystal obtained by such Chokura le ski method,
Obtain a plate-shaped wafer was polished until both sides of the wafer to a predetermined thickness and then fixed to the upper platen of stainless steel or ceramic, mirror polished on one side poly <br/> petri using colloidal silica After polishing, remove from the upper surface plate,
It is obtained by washing with an organic solvent. Since the wafer is fixed to the upper platen using wax, heating at 80 to 120 ° C. is indispensable at the time of desorption of the wafer.

[0003]

In the thus obtained lithium niobate single crystal substrate, a local strain field of about 20 μm is observed over the entire surface.
Changes in the refractive index and scattering due to the strain field occur and cannot be used as a good substrate. An object of the present invention is to provide a method for manufacturing a single crystal substrate having no strain field.

[0004]

As a result of various studies, the inventor of the present invention has found that the above-mentioned strain field is generated in a polishing step, and has reached the present invention. That is, the method according to the first aspect of the present invention, which solves the above-described problem, cuts a single crystal of lithium niobate to obtain a plate-like wafer, and polishes the plate-like wafer with a double-sided lap to a desired thickness. In a method of obtaining a lithium niobate single crystal substrate by mirror polishing one side of a plate-like wafer using a single-side polisher, the plate-like wafer wrapped on both sides is provided on an upper platen and is thinner than the thickness of the plate-like wafer. A mirror polishing using the single-sided polisher while holding the polishing pad at a temperature of 60 ° C. or less while holding the wafer in a recess of a wafer carrier having a recess large enough to accommodate a plate-like wafer on its surface. It is characterized by. Further, the method according to the second aspect of the present invention for solving the above-mentioned problem is to cut a lithium niobate single crystal to obtain a plate-like wafer, and to polish the plate-like wafer with a double-sided lap to a desired thickness. In a method for obtaining a lithium niobate single crystal substrate by mirror-polishing both surfaces of the plate-like wafer using a double-sided polisher, the temperature of the polishing cloth is set to 60 ° C.
Mirror polishing is performed using the double-sided polisher while maintaining the following conditions. Furthermore, the method according to the invention of claim 3 and 4, wherein solving the above-also claim 1
Is a method for obtaining a lithium niobate single crystal substrate according to 2.
Mirror polishing is performed while maintaining the temperature of the polishing cloth at 30 ° C. or lower.

[0005]

As a result of various studies, the present inventors have found that the temperature applied to a wafer during polishing is related to the number of local strain fields (hereinafter, simply referred to as strain fields). 1, both surfaces thereof, while maintaining the polishing cloth 30 ° C. The wafer of thickness 800μm obtained by mirror polishing placed on a stainless steel plate, allowed to cool after heating to a predetermined temperature, the strain field in a polarizing microscope A graph showing the relationship between the heating temperature obtained by counting the number and the number of strain fields .
It is a rough figure .

FIG. 1 shows that when the heating temperature exceeds 60 ° C., the strain field rapidly increases. The heating temperature is 60
Even if the temperature exceeds ℃, the strain field can be eliminated by slow cooling, but in this case, it is not practical because slow cooling is required over, for example, 20 hours or more.

[0007]

The present invention will be further described below with reference to examples.

(Example 1) After cutting a lithium niobate single crystal into a C-plate wafer having a diameter of 3 inches and a thickness of 850 μm,
Polishing was performed to a thickness of 800 μm by double-sided lapping using GC # 1000 and # 2000 to remove damage at the time of cutting and adjust the plate thickness. Next, an FR having a thickness of 300 to 600 μm provided with a recess having an inner diameter slightly larger than 3 inches
A wafer carrier made of P is adhered to an upper plate made of ceramic, and the polished C plate wafer is mounted in the concave portion thereof.
This was placed on a polishing cloth with a single-side polisher, and pressure was applied to the upper platen to perform mirror polishing. Colloidal silica was used as the abrasive, and the temperature and amount of the cooling water were adjusted so that the temperature of the polishing cloth was 30 ° C. or less. Polishing time is 20 minutes, allowance is 1
It was 0 μm. After polishing, the C-plate wafer was removed from the wafer carrier, washed with water, and dried with a spinner. When the obtained C-plate wafer, that is, a lithium niobate single crystal substrate was examined, no strain field was detected.

Example 2 A C-plate wafer was prepared in the same manner as in Example 1 except that a polishing machine was a double-sided polisher and the polishing time was 30 minutes, and the presence or absence of a strain field was examined.
There was no strain field in the resulting C-plate wafer, ie, the lithium niobate single crystal substrate.

[0010]

According to the method of the present invention, a lithium niobate single crystal substrate having no strain field can be obtained. The method of the present invention is particularly useful for an optical element or a lithium niobate single crystal for a surface acoustic wave filter. It is effective for manufacturing substrates.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the heating temperature and the number of strain fields obtained by studying the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21/304

Claims (4)

(57) [Claims] 1. A single wafer of lithium niobate is cut to obtain a plate-like wafer, and the plate-like wafer is polished to a desired thickness with a double-sided lap, and then one side of the plate-like wafer is mirror-polished using a single-side polisher. In the method of obtaining a lithium niobate single crystal substrate, the double-sided wrapped plate-like wafer is provided on an upper platen, is thinner than the thickness of the plate-like wafer, and is large enough to accommodate the plate-like wafer on its surface. A method of manufacturing a single crystal lithium niobate substrate, wherein the single-sided polisher is mirror-polished while being housed in a concave portion of a wafer carrier having a concave portion and maintaining the temperature of the polishing cloth at 60 ° C. or lower. . 2. A plate-like wafer is obtained by cutting a lithium niobate single crystal, and the plate-like wafer is polished to a desired thickness by a double-sided lap, and then both surfaces of the plate-like wafer are mirror-polished using a double-sided polisher. A method for obtaining a lithium niobate single crystal substrate, wherein mirror polishing is performed using the double-sided polisher while maintaining the temperature of the polishing cloth at 60 ° C. or lower. 3. A plate-shaped lithium niobate single crystal is cut.
A wafer is obtained, and the plate-shaped wafer is wrapped on both sides in a desired thickness.
And then use a single-side polisher to remove the wafer
Mirror-polished one side of the substrate to obtain a lithium niobate single crystal substrate.
The method of obtaining, wherein the plate-like wafer wrapped on both sides is provided.
On the upper platen and thinner than the thickness of the plate wafer.
And large enough to accommodate a plate-like wafer on its surface.
Stored in the recess of a wafer carrier having a recess,
First, while maintaining the temperature of the polishing cloth at 30 ° C. or less,
A method for producing a lithium niobate single crystal substrate, wherein mirror polishing is performed using a Lisher . 4. A plate-like material obtained by cutting a lithium niobate single crystal.
A wafer is obtained, and the plate-shaped wafer is wrapped on both sides in a desired thickness.
And then use a double-sided polisher to make
Mirror-polished both sides of the eher and lithium niobate single crystal base
In the method of obtaining a plate, the temperature of the polishing cloth is maintained at 30 ° C or less.
While performing mirror polishing using the double-sided polisher.
And a method for producing a lithium niobate single crystal substrate.