JP2836763B2 - NdGaO (3) Single crystal etching method - Google Patents

Description

The present invention relates to a promising NdGa as a substrate for an oxide superconducting thin film.
The present invention relates to a method for etching an O ₃ single crystal.

Conventional technology NdGaO ₃ single crystal has a small lattice mismatch with the oxide superconductor, a similar coefficient of thermal expansion, a similar crystal structure, and no phase transformation from room temperature to 1000 ° C. It has excellent properties as a substrate for epitaxial growth of superconducting thin films.

The NdGaO ₃ single crystal is grown and cut and polished by the Czochralski method. In these steps, crystallographic disorder called a work-affected layer generated on the crystal surface or a defect contained in the grown crystal itself deteriorates the quality of a thin film epitaxially grown thereon. Evaluation of crystal defects is generally performed by etching the crystal surface using an etchant such as an acid, depositing etch pits, and comparing the densities.

Problems to be Solved by the Invention However, in the etching of a novel oxide such as NdGaO ₃ single crystal, an appropriate etching solution and etching conditions for depositing etch pits on the crystal surface have not been found, and the single crystal This was an obstacle in evaluating crystallinity.

The inventors of the present invention have made intensive studies and, as a result, have made the following invention.

Means and Action for Solving the ProblemsThe present inventors have studied an etching method of NdGaO ₃ single crystal used as a substrate for an oxide superconducting thin film, and as a result, using phosphoric acid as an etching solution, and adjusting the temperature of the etching solution to 100 It has been found that etch pits can be deposited on the crystal surface by setting the temperature to ~ 230 ° C. Hereinafter, the contents of the present invention will be described in detail.

Oxides such as NdGaO ₃ single crystals hardly elute in an etchant such as an acid at room temperature. Therefore, it is necessary to increase the temperature of the etchant to accelerate the reaction. In order to sufficiently increase the reaction rate, it is necessary to select an etching solution having a high boiling point. The boiling points of hydrochloric acid, hydrofluoric acid, and nitric acid are about 120 ° C., and the temperatures cannot be raised sufficiently. On the other hand, phosphoric acid is dehydrated by heating, but does not boil and can be heated to 400 ° C. or higher, and NdGaO ₃
Suitable as a single crystal etchant.

When phosphoric acid is used as an etchant, the temperature is 100 ° C
Below, the etching rate is too slow to be practical. Therefore, it is desirable to select a temperature according to a desired etching rate in a range of 100 ° C. or more.

When performing the etching, if the temperature is 230 ° C. or less, pits are generated on the crystal surface. It is considered that this is because the etching process is rate-determining, so that the defective portion of the crystal is selectively etched.

On the other hand, when the temperature is higher than 230 ° C., no pits are formed on the crystal surface. This is probably because the elution rate of NdGaO ₃ was increased, the etching process became diffusion-controlled, and the crystal surface was uniformly etched.

Thus, by setting the temperature of the etching solution to 100 to 230 ° C., etch pits can be deposited on the crystal surface.

Example An NdGaO ₃ single crystal was grown by the Czochralski method. This crystal was cut into a size of 10 mm × 10 mm × 0.5 mm parallel to the (110) plane, and was mirror-finished by mechanical polishing. The crystals were etched with phosphoric acid at 200 ° C. for 5 minutes.
At this time, pits were formed on the crystal surface as shown in Reference Photo 1.

Comparative Example 1 When the same sample as in the example was etched with phosphoric acid at 300 ° C. for 5 minutes, no pits were generated on the crystal surface as shown in Reference Photo 2.

Comparative Example 2 When the same sample as the example was etched with phosphoric acid at 30 ° C. for 6 hours, the amount of etching on the crystal surface was 1 μm or less.
The etching rate was very slow.

Effect of the Invention As described above, according to the present invention, an etch pit can be generated on the surface of an NdGaO ₃ single crystal and defects can be easily found, which contributes to the evaluation of a substrate for an oxide superconducting thin film.

Claims (2)

(57) [Claims] An NdGaO ₃ single crystal is etched using phosphoric acid as an etchant when etching the surface thereof.
GaO ₃ single crystal etching method. 2. The method for etching a NdGaO ₃ single crystal according to claim 1, wherein an etching pit is deposited on the crystal surface at a temperature of the etching solution of 100 to 230 ° C.