JP3649786B2 - Treatment liquid for perovskite type single crystal and processing method for perovskite type single crystal - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a processing solution for a perovskite structure single crystal and a method for processing a perovskite structure single crystal. In particular, the present invention relates to a processing solution for a rare earth 13 (3B) group perovskite structure single crystal and a processing method thereof, which are promising as substrates for GaN-based blue semiconductor materials and superconducting materials.
[0002]
[Prior art]
Recently, a gallium nitride compound semiconductor (In _x Ga _y Al _1-xy N (0 ≦ x, y; x + y ≦ 1)) has attracted attention as a blue semiconductor light emitting device. When a gallium nitride compound semiconductor crystal is grown on a sapphire (α-Al ₂ O ₃ ) substrate, the (0001) plane of the gallium nitride compound semiconductor crystal is generally grown on the (0001) plane of sapphire. In this case, the deviation of the lattice constant was 16%, and a gallium nitride compound semiconductor crystal having excellent crystallinity could not be grown. As a solution,
(1) A method of growing a gallium nitride-based compound semiconductor crystal after first growing a buffer layer (for example, an AlN buffer layer or a GaAlN buffer layer) on a sapphire substrate (Japanese Patent Publication S59-48794, JP H4-297023),
(2) As a single crystal substrate, a crystal having a crystal structure and lattice constant as close as possible to those of a gallium nitride compound semiconductor single crystal (for example, aluminum garnet (ReAl ₂ Al ₃ O ₁₂ ) or gallium garnet (ReAl ₂ Ga ₃ O ₁₂ )) JP, S49-3899), a method using MgO, ZnO, CaO, etc. (JP H04-209577)),
It has been known. However, there are problems with lattice matching with the substrate, thermal stability of the substrate, and the like, and the present applicant has proposed a rare earth 13 (3B) group perovskite structure single crystal.
[0003]
In addition, rare earth 13 (3B) group perovskite structure single crystal NdGaO ₃ single crystal is also known to be a promising material as a substrate for oxide superconductivity (for example, Applied Physics Letters, Vol. 54). P1054-1056).
[0004]
As described above, the perovskite structure single crystal is a very promising material as a blue semiconductor light emitting device material and other superconducting materials. In particular, as the perovskite structure single crystal, the rare earth 13 (3B) group is a rare earth 13 (3B) group perovskite structure in which the rare earth 13 (3B) group is at least one of aluminum, gallium and indium, particularly its {110} plane, {011} plane , {101} plane is preferably used.
[0005]
[Problems to be solved by the invention]
Before such a thin film is formed on a perovskite structure single crystal substrate, it is necessary to process the substrate once in order to remove the work-affected layer on the substrate surface. The work-affected layer is a layer having a distorted atomic arrangement introduced when the substrate is polished, and usually has a thickness of about 1 to 10 μm. As a method for treating the surface of an NdGaO ₃ substrate, it is known to treat the surface with phosphoric acid at a temperature of 100 to 230 ° C. (Japanese Patent Laid-Open No. H04-202100). However, this processing solution has the following problems.
[0006]
(1) If the temperature of the treatment liquid is 100 ° C. or lower, the etching rate is slow and is not practical.
(2) When the temperature of the processing solution is 100 ° C. to 230 ° C., etch pits are generated by etching.
(3) When the temperature of the treatment liquid is 230 ° C. or higher, the etching rate is too high to control the treatment, and there are industrial and safety problems.
[0007]
If a film is grown on the substrate with the work-affected layer remaining on the substrate surface, the quality of the film deteriorates.On the other hand, when a film is formed on a substrate on which etch pits have been generated, Abnormal growth occurs.
[0008]
[Means for Solving the Problems]
Therefore, the present inventors have intensively studied a suitable treatment liquid for the perovskite structure single crystal substrate, and have reached the present invention. That is, the present invention is characterized in that a perovskite type structure single crystal treatment liquid and a perovskite type structure single crystal, which are composed of a mixed liquid of phosphoric acid and aqua regia, are treated with a mixed liquid of phosphoric acid and aqua regia. This is a method for processing a perovskite type single crystal. Further, the perovskite structure single crystal treatment is characterized in that the perovskite structure is a rare earth 13 (3B) group perovskite structure, and the rare earth 13 (3B) group is at least one of aluminum, gallium and indium. It is a liquid.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
A smooth substrate surface suitable for epitaxial growth can be obtained by treating the perovskite structure single crystal with a treatment liquid composed of a mixture of phosphoric acid and aqua regia. The appropriate mixing ratio depends on the processing temperature. For example, at a processing temperature of about 60 ° C., too much phosphoric acid tends to generate etch pits, and too little phosphoric acid results in a slow etching rate.
[0010]
【Example】
As an example, an example is shown in which a (101) plane of an NdGaO ₃ substrate as a perovskite structure substrate is treated with each treatment solution, and then a gallium nitride based semiconductor film is grown thereon.
[0011]
(Example)
The (101) plane NdGaO ₃ substrate was immersed in a treatment solution of phosphoric acid: aqua regia (HCl / HNO ₃ = 3/1) = 1: 3 (volume ratio) at 60 ° C. for 15 minutes. The NdGaO ₃ substrate was etched by about 4 μm. Etch pits were not observed when the surface was observed with an optical microscope.
[0012]
This substrate was washed and dried, and set in a hydride VPE apparatus. While flowing nitrogen gas, the temperature of the substrate portion was 900 ° C., Ga was used as the gallium raw material, and the temperature of the gallium raw material was 850 ° C. A chloride gas diluted with nitrogen gas was flowed from the upstream of the gallium raw material, and at the same time, the gallium raw material was bypassed and ammonia gas was flowed immediately before the substrate to form a GaN film on the substrate for 30 minutes. The thickness of the obtained GaN film was about 3 μm, and no abnormal grain growth was observed.
[0013]
(Comparative example)
The (101) plane NdGaO ₃ substrate was immersed in a treatment solution of phosphoric acid: sulfuric acid = 1: 3 (volume ratio) at 130 ° C. for 15 minutes. The NdGaO ₃ substrate was etched by about 4 μm. When the surface was observed with an optical microscope, many etch pits were observed.
[0014]
This substrate was washed and dried, and a GaN film was formed by hydride VPE in the same manner as in the example. Although the thickness of the obtained GaN film was about 3 μm, many abnormal grain growths were observed.
[0015]
【The invention's effect】
Perovskite structure single crystal, rare earth 13 (3B) group perovskite structure, especially rare earth 13 (3B) group aluminum, gallium and indium perovskite structure single crystal using treatment liquid composed of phosphoric acid and aqua regia By processing this, a smooth processed surface can be obtained.

Claims (6)

A processing solution for a perovskite structure single crystal, characterized by comprising a mixed solution of phosphoric acid and aqua regia. The processing solution for a perovskite structure single crystal according to claim 1, wherein the perovskite structure is a rare earth 13 (3B) group perovskite structure. 3. The processing solution for a perovskite structure single crystal according to claim 2, wherein the rare earth 13 (3B) group is at least one of aluminum, gallium and indium. A method for treating a perovskite structure single crystal, comprising treating the perovskite structure single crystal with a mixture of phosphoric acid and aqua regia. 5. The method for treating a perovskite structure single crystal according to claim 4, wherein the perovskite structure is a rare earth 13 (3B) group perovskite structure. 6. The method for processing a perovskite structure single crystal according to claim 5, wherein the rare earth 13 (3B) group is at least one of aluminum, gallium and indium.