PROBLEM TO BE SOLVED: To obtain a porous body having fine pores of high density without adding complicated processes by mounting an anodized alumina as a mask on a diamond substrate and subjecting the substrate to plasma etching.
SOLUTION: Pores are formed in a substrate with the same arrangement as that of pores in the mask. As for the anodized alumina, an alumina having pores of 5 to 400 nm pore diameter in hexagonal close-packed arrangement with 100 to 500 nm distance of pores is used. With 1 to 0.1 μm thickness of the alumina, good results can be obtd. As for the substrate, a single crystal or polycrystal diamond which is a natural product or synthesized can be used. The substrate 3 on which the anodized alumina 1 is mounted is disposed on a plasma electrode 4 and subjected to plasma etching. During the process, by adding oxygen to the plasma excitation gas, the etching rate can be significantly improved. Then the mask is dissolved and removed with a soln. such as sodium hydroxide having solubility with the anodized alumina.