Patent ID: 8384111

Claim:
A method for forming a sapphire substrate, the method comprising the steps of: (A) depositing a metal by evaporation on a surface of a thin sapphire plate; (B) performing heat treatment on the thin sapphire plate, thereby changing the metal into a fine particle state, after step A; and (C) etching the surface of the thin sapphire plate using the metal in the fine particle state as a mask to simultaneously remove the fine metal particles and to form convex shapes under the locations of the fine metal particles, wherein each of the convex shapes is tapered from a bottom thereof to a top thereof, the convex shapes are arranged at a density of 1×10 5 /cm 2 to 5×10 7 /cm 2 , both inclusive, a flat portion of the top of each of the convex shapes has an area larger than 0 and smaller than or equal to 10 μm 2 , and a bottom surface of each of the convex shapes has a longer diameter of 1 μm to 50 μm, both inclusive, and a shorter diameter of 100 nm to 10 μm, both inclusive.